Category Archives: Astronomy

The Cosmic Microwave Background Provides a Refined View of Our Universe

Peter Lobner, 12 January 2021

The Atacama Cosmology Telescope (ACT) is a six-meter (19.7 foot) radio telescope designed to make high-resolution, microwave-wavelength surveys of the cosmic microwave background (CMB).  It is located at a remote site in the Atacama Desert at an elevation of 5,190 meters (17,030 feet) in northern Chile. 

The ACT site.  Source: ACT Collaboration

ACT observes in three frequency bands (148, 218 and 277 GHz) and has a resolution of 1.3 arc minutes at 148 GHz, near the peak of the CMB spectrum.  This is significantly higher than the 5-10 arc minute resolution of the Planck spacecraft, which observed the CMB from 2009 to 2013 in the frequency range from 30 to 857 GHz. You’ll find a detailed description of the Atacama Cosmology Telescope (ACT) at the following link: https://www.cosmos.esa.int/documents/387566/387653/Ferrara_Dec3_09h20_Devlin_ACT.pdf

I reported on key results of the Planck CMB survey results in my post at the following link: https://lynceans.org/all-posts/the-universe-is-isotropic/

New results from the ACT survey, reported in December 2020, affirm the Planck CMB survey results.  

  • The universe is isotropic
  • The estimate of the age of the universe was refined to 13.77 billion years old ± 0.04 billion years, overlapping uncertainty bands with the 2015 Planck estimate of 13.813 ± 0.038 billion years
  • The value of the Hubble constant was refined to 67.6 kilometers / second / megaparsec, up slightly from the 2018 Planck estimate of 67.4 kilometers / second / megaparsec.  The significant difference from the value derived from astrophysical measurements, 73.5 km / second / megaparsec, remains unexplained.
ACT high resolution image of the isotropic cosmic background radiation covering a section of the sky 50 times the width of a full moon. This image represents a region of space 20 billion light-years across. Source: ACT Collaboration via EarthSky

For more information:

Japan’s Hayabusa2 Spacecraft Returns Asteroid Material to Earth

Peter Lobner

Japan’s Hayabusa2 (Japanese for Peregrine falcon 2) spacecraft returned from its six-year mission to asteroid 162173 Ryugu for a high-speed fly-by of Earth on 5 December 2020, during which it released a reentry capsule containing the material collected during two separate sampling visits to the asteroid’s surface.  The capsule successfully reentered Earth’s atmosphere, landed in the planned target area in Australia’s Woomera Range and was recovered intact.  The sample return capsule is known as the “tamatebako” (treasure box).

Location of Woomera Range.  Source: itea.org
Hayabusa2’s sample return capsule after landing in the Woomera Range, Australia.  
Source: JAXA
Capsule containing samples from asteroid Ryugu.  Source: JAXA

Background

The first asteroid sample return mission was Japan’s Hayabusa1, which was launched on 9 May 2003 and rendezvoused with S-type asteroid 25143 Itokawa in mid-September 2005. A small sample was retrieved from the surface on 25 November 2005. The sample, comprised of tiny grains of asteroidal material, was returned to Earth on 13 June 2010, with a landing in the Woomera Range.

Japan’s Hayabusa2 and the US OSIRIS-Rex asteroid sample return missions overlap, with Hayabusa2 launching about two years earlier and returning its surface samples almost three years earlier.  Both spacecraft were orbiting their respective asteroids from 31 December 2018 to 12 November 2019.

You’ll find a great deal of information and current news on the Hayabusa2 and OSIRIS-REx asteroid sample return missions on their respective project website:

The Hayabusa2 extended mission

An extended mission to explore additional asteroids was made possible by the excellent health of the Hayabusa2 spacecraft and the economic use of fuel during the basic mission.  Hayabusa2 still has 30 kg (66 lb) of xenon propellant for its ion engines, about half of its initial load of 66 kg (146 lb).

As of September 2020, JAXA’s plans are is to target the Hayabusa2 spacecraft for the following two asteroid encounters: 

  • Conduct a high-speed fly-by of L-type asteroid (98943) 2001 CC21 in July 2026.  This asteroid has a diameter between 3.47 to 15.52 kilometers (2.2 to 9.6 miles).
  • Continue on a rendezvous with asteroid 1998 KY26 in July 2031.  This is a 30-meter (98-foot) diameter asteroid, potentially X-type (metallic), and rotating rapidly with a period of only 10.7 minutes.
Computer model view of 1998 KY26 based on radar data from Goldstone observatory.  Source: NASA/JPL via Wikipedia

You’ll find more information on the extended mission on the Hayabusa project website here:  https://www.hayabusa2.jaxa.jp/en/galleries/othermovie/pages/ext_mission_en.html

For more information:

Adieu to Radio Astronomy at Arecibo

Peter Lobner, Updated 15 January 2021

The Arecibo Observatory (AO) on Puerto Rico has been out of service since 10 August 2020, when a three-inch auxiliary support cable slipped out of its socket and fell onto the fragile radio telescope dish below. Three months later, on 6 November 2020, a second cable associated with the same support tower broke, damaging nearby cables, causing more damage to the reflector dish, and leaving the radio telescope’s support structure in a weakened and uncertain state.

On 19 November 2020, the National Science Foundation (NSF) announced it has begun planning for decommissioning the 57-year old Arecibo Observatory’s (AO) 1,000-foot (305-meter) radio telescope due to safety concerns after the two support wires broke and seriously damaged the antenna.  You can read NSF News Release 20-010 at the following link: https://www.nsf.gov/news/news_summ.jsp?cntn_id=301674

The 1,000-foot (305-m) dish at Arecibo Observatory in better days, in Spring 2019. Source: AO/University of Central Florida (UCF)
The damaged Arecibo Observatory radio telescope in November 2020.  
Source: NSF
A view from under the damaged dish. 
Source: AO/University of Central Florida (UCF)

The NSF website for AO is at the following link:  https://www.naic.edu/ao/telescope-description

This website includes a timeline summarizing the most important discoveries made by AO since 1967: https://www.naic.edu/ao/legacy-discoveries

Not included in the NSF timeline is the 1974 first-ever broadcast into deep space of a powerful signal that could alert other intelligent life to our technical civilization on Earth. The 1,679 bit “Arecibo Message” was directed toward the globular star cluster M13, which is 22,180 light years away. The message will be in transit for another 22,134 years.

The Arecibo Message. Source:  SETI

You’ll find a description of the Arecibo Message on the SETI website here: https://www.seti.org/seti-institute/project/details/arecibo-message

A key capability lost is AO’s planetary radar capability that enabled the large dish to function as a high-resolution, active imaging radar.  You’ll find examples of AO’s radar images of the Moon, planets, Jupiter’s satellites, Saturn’s rings, asteroids and comets on the NSF website here:  https://www.naic.edu/~pradar/radarpage.html

More impressive than the still images were animations created from a sequence of AO radar images, particularly of passing asteroids.  The animations defined the motion of the object as it flew near Earth. As an example, you can watch the following short (1:07 minutes) video, “Big asteroid 1998 OR2 seen in radar imagery ahead of fly-by”:

The US still has a reduced capability for planetary radar imaging with NASA’s Deep-Space Network’s Uplink Array.

AO’s radio telescope dish was the largest in the world until 2016 when China completed its 500-meter (1,640-foot) FAST radio telescope. It looks like the torch was passed just in time.  You’ll find information on FAST here: https://lynceans.org/all-posts/chinas-five-hundred-meter-aperture-spherical-telescope-fast-will-be-the-worlds-largest-radio-telescope/

Arecibo was not part of the Event Horizon Telescope (EHT) Collaboration of worldwide radio telescopes that succeeded in imaging the shadow of a black hole in 2019.  You’ll find this story here: https://lynceans.org/all-posts/the-event-horizon-telescope-team-has-produced-the-first-image-showing-the-shadow-of-a-black-hole/

The 19 November 2020 NSF news release stated, “After the telescope decommissioning, NSF would intend to restore operations at assets such as the Arecibo Observatory LIDAR facility — a valuable geospace research tool — as well as at the visitor center and offsite Culebra facility, which analyzes cloud cover and precipitation data.”

Adieu to radio astronomy at Arecibo.

Update 1 December 2020: Arecibo radio telescope collapsed.

NPR reported, “The Arecibo Observatory in Puerto Rico has collapsed, after weeks of concern from scientists over the fate of what was once the world’s largest single-dish radio telescope. Arecibo’s 900-ton equipment platform, suspended 500 feet above the dish, fell overnight after the last of its healthy support cables failed to keep it in place. No injuries were reported, according to the National Science Foundation, which oversees the renowned research facility.”

Arecibo after the collapse. Source: Ricardo Arduengo / AFP via Getty Images

Update 8 December 2020: National Science Foundation video shows the moment of collapse.

For more information:

The Moon has Never Looked so Colorful

Peter Lobner

On 20 April 2020, the U.S. Geological Survey (USGS) released the first-ever comprehensive digital geologic map of the Moon.  The USGS described this high-resolution map as follows:

“The lunar map, called the ‘Unified Geologic Map of the Moon,’ will serve as the definitive blueprint of the moon’s surface geology for future human missions and will be invaluable for the international scientific community, educators and the public-at-large.”

Color-coded orthographic projections of the “Unified Geologic Map of the Moon” showing the geology of the Moon’s near side (left) and far side (right).  Source:  NASA/GSFC/USGS

You’ll find the USGS announcement here:  https://www.usgs.gov/news/usgs-releases-first-ever-comprehensive-geologic-map-moon

You can view an animated, rotating version of this map here:  https://www.youtube.com/watch?v=f2Nt7DxUV_k

This remarkable mapping product is the culmination of a decades-long project that started with the synthesis of six Apollo-era (late 1960s – 1970s) regional geologic maps that had been individually digitized and released in 2013 but not integrated into a single, consistent lunar map. 

This intermediate mapping product was updated based on data from the following more recent lunar satellite missions:

  • NASA’s Lunar Reconnaissance Orbiter (LRO) mission:
    • The Lunar Reconnaissance Orbiter Camera (LROC) is a system of three cameras that capture high resolution black and white images and moderate resolution multi-spectral images of the lunar surface: http://lroc.sese.asu.edu
    • Topography for the north and south poles was supplemented with Lunar Orbiter Laser Altimeter (LOLA) data: https://lola.gsfc.nasa.gov
  • JAXA’s (Japan Aerospace Exploration Agency) SELENE (SELenological and ENgineering Explorer) mission:

The final product is a seamless, globally consistent map that is available in several formats: geographic information system (GIS) format at 1:5,000,000-scale, PDF format at 1:10,000,000-scale, and jpeg format.

At the following link, you can download a large zip file (310 Mb) that contains a jpeg file (>24 Mb) with a Mercator projection of the lunar surface between 57°N and 57°S latitude, two polar stereographic projections of the polar regions from 55°N and 55°S latitudes to the poles, and a description of the symbols and color coding used in the maps.

https://astrogeology.usgs.gov/search/map/Moon/Geology/Unified_Geologic_Map_of_the_Moon_GIS_v2

These high-resolution maps are great for exploring the lunar surface in detail. A low-resolution copy (not suitable for browsing) is reproduced below.

For more information on the Unified Geologic Map of the Moon, refer to the paper by C. M. Fortezzo, et al., “Release of the digital Unified Global Geologic Map of the Moon at 1:5,000,000-scale,” which is available here:  https://www.hou.usra.edu/meetings/lpsc2020/pdf/2760.pdf

Working Toward a More Detailed View of a Black Hole

Peter Lobner

1.  Introduction

The Event Horizon Telescope (EHT) Collaboration reported a great milestone on 10 April 2019 when they released the first synthetic image showing a luminous ring around the shadow of the M87 black hole.

First synthetic image of the M87 black hole.
Source: Event Horizon Telescope Collaboration

The  bright emission ring surrounding the black hole was estimated to have an angular diameter of about 42 ± 3 μas (microarcseconds), or 1.67 ± 0.08 e-8 degrees, at a distance of 55 million light years from Earth.  At the resolution of the EHT’s first black hole image, it was not possible to see much detail of the ring structure.   

Significantly improved telescope performance is required to discern more detailed structures and, possibly, time-dependent behavior of spacetime in the vicinity of a black hole.  The EHT Collaboration has a plan for improving telescope performance.  A challenging new observational goal has been established by scientists who recently postulated the existence of a “photon ring” around a black hole.  Let’s take a look at these matters.

2. Improving the performance of the EHT terrestrial observatory network

As I described in my 3 March 2017 post on the EHT, a very long baseline interferometry (VLBI) array with the diameter of the Earth (12,742 km, 1.27e+7 meters) operating in the EHT’s millimeter / submillimeter wavelength band (1.3 mm to 0.6 mm) has a theoretical angular resolution of 25 to 12 μas, with the better resolution at the shorter wavelength.

The EHT team plans to improve telescope performance in the following key areas:

Improve the resolution of the EHT

  • Observe at shorter wavelengths:  The EHT’s first black hole image was made at a wavelength of 1.3 mm (230 GHz). Operating the telescopes in the EHT array at a shorter wavelength of 0.87 mm (frequency of 345 GHz) will improve angular resolution by about 40%.  This upgrade is expected to start after 2020 and take 3 – 5 years to deploy to all EHT observatories.
  • Extend baselines: Adding more terrestrial radio telescopes will lengthen some observation baselines, up to the limit of the Earth’s diameter. 

Improve the sensitivity of the EHT

  • Collect data at multiple frequencies (wide bandwidth): Black holes emit radiation at many frequencies.  EHT sensitivity and signal-to-noise ratio can be improved by increasing the number of frequencies that are monitored and recorded during EHT observations.  This requires multi-channel receivers and faster, more capable data processing and recording systems at all EHT observatories. 
  • Increase the EHT aperture:  The EHT team notes that the most straightforward way to boost the sensitivity of the EHT is to increase the net collecting area of the dishes in the array.  You can all of the observatories participating in EHT here:  https://eventhorizontelescope.org/blog/global-web-tour-eht-observatories

The size of individual radio telescopes in the EHT array vary from the 12 m Greenland Telescope with an aperture of about 113 square meters to the 50 m Large Millimeter Telescope (LMT) in Mexico with an aperture of about 2,000 square meters.  

  • The telescope with the largest aperture is the phased ALMA array, which is comprised of up to 54 x 12 m telescopes with a effective aperture of about 7,200 square meters.  The Greenland Telescope originally was a prototype for the ALMA array and was relocated to Greenland to support VLBI astronomy.
  • A phased array is an effective solution for VLBI observations because the requirements for mechanical precision and rigidity of the dish are easier to meet with a smaller radio telescope dish that can be manufactured in large numbers.

With higher angular resolution and improved sensitivity, and with more powerful signal processing to handle the greater volume of data, it may be possible for the EHT to “see” some detailed structures around a black hole.  Multiple images of a black hole over a period of time could be used to create a dynamic set of images (i.e., a short “video”) that reveal time-dependent black hole phenomena.    

You’ll find more information on these telescope system upgrades on the EHT website here:(https://eventhorizontelescope.org/technology).

3. Photon ring:   New insight into the fine structure in the vicinity of a black hole

On 18 March 2020, a team of scientists postulated the existence of a “photon ring” closely orbiting a black hole.  The scientists further postulated that the “glow” from the first few photon sub-rings may be directly observable with a VLBI array like the EHT. 

Time-averaged results of computer simulations of the photon ring surrounding the M87 black hole.  
Source:  Michael Johnson, et al., 18 March 2020

The abstract and part of the summary of the paper are reproduced below.

  • Abstract:  “The Event Horizon Telescope image of the supermassive black hole in the galaxy M87 is dominated by a bright, unresolved ring. General relativity predicts that embedded within this image lies a thin “photon ring,” which is composed of an infinite sequence of self-similar subrings that are indexed by the number of photon orbits around the black hole. The subrings approach the edge of the black hole “shadow,” becoming exponentially narrower but weaker with increasing orbit number, with seemingly negligible contributions from high-order subrings. Here, we show that these subrings produce strong and universal signatures on long interferometric baselines. These signatures offer the possibility of precise measurements of black hole mass and spin, as well as tests of general relativity, using only a sparse interferometric array.”
  • Summary: “In summary, precise measurements of the size, shape, thickness, and angular profile of the nth photon subring of M87 and Sgr A* may be feasible for n = 1 (the first ring) using a high-frequency ground array or low Earth orbits, for n = 2 (the second ring) with a station on the Moon, and for n = 3 (the third ring) with a station in L2 (Lagrange Point).”
Five Lagrange points in the Earth-Sun system. 
L2 is behind the Earth.  Source: NASA

The complete, and quite technical, 18 March 2020 paper by Michael Johnson, et al., “Universal interferometric signatures of a black hole’s photon ring,” is available on the Science Advances website here:  https://advances.sciencemag.org/content/6/12/eaaz1310

You’ll find a more narrative summary by Camille Carlisle, writing for SkyandTelescope.com, here:  https://skyandtelescope.org/astronomy-news/scientists-predict-countless-rings-of-light-encircle-black-holes/

The following short video (1:05 minutes) from the Center for Astrophysics | Harvard & Smithsonian shows an animation of photon behavior in the vicinity of a black hole and the formation of a photon ring.

The creators of the video explain: 

  • “Black holes cast a shadow on the image of bright surrounding material because their strong gravitational field can bend and trap light. The shadow is bounded by a bright ring of light, corresponding to photons that pass near the black hole before escaping.”
  • “The ring is actually a stack of increasingly sharp subrings, and the n-th subring corresponds to photons that orbited the black hole n/2 times before reaching the observer. This animation shows how a black hole image is formed from these subrings and the trajectories of photons that create the image.”

4.  EHT images black hole-powered relativistic jets

On 7 April, 2020, the EHT Collaboration reported that it had produced images with the finest detail ever seen of relativistic jets produced by a supermassive black hole.  The target of their observation was Quasar 3C 279, which contains a black hole about one billion times more massive than our Sun, and is about 5 billion light-years away from Earth in the constellation Virgo.  

With a resolution of 20 μas (microarcseconds) for observations at a wavelength of 1.3 mm, the EHT imaging revealed that two relativistic jets existed.  As shown in the following figure, lower resolution imaging by the Global 3mm VLBI Array (GMVA) and a VLBI array observing at 7 mm wavelength did not show two distinct jets. 

Illustration of multi-wavelength 3C 279 jet structure in April 2017.
The observing dates, arrays, and wavelengths are noted at each panel. Source: J.Y. Kim (MPIfR), Boston University Blazar Program (VLBA and GMVA), and Event Horizon Telescope Collaboration

In their 7 April 2020 press release, the EHT Collaboration reported:  “For 3C 279, the EHT can measure features finer than a light-year across, allowing astronomers to follow the jet down to the accretion disk and to see the jet and disk in action. The newly analyzed data show that the normally straight jet has an unexpected twisted shape at its base and revealing features perpendicular to the jet that could be interpreted as the poles of the accretion disk where the jets are ejected. The fine details in the images change over consecutive days, possibly due to rotation of the accretion disk, and shredding and infall of material, phenomena expected from numerical simulations but never before observed.”

Time-dependent behavior of the two relativistic jets from 
Quasar 3C 279.  Source:  Screenshot from 
Event Horizon Telescope Collaboration video

The following short video (1:14 minutes) from the EHT Collaboration shows the 3C 279 quasar jets and their motion over the course of one week, from 5 April to 11 April 2017, as observed by the EHT.

5. Adding space-based EHT observatories

Imaging the M87 photon ring will be a challenging goal for future observations with an upgraded EHT.  As indicated in the paper by Michael Johnson, et al., an upgraded terrestrial EHT array may be able to “see” the first photon sub-ring.  However, space-based telescopes will be needed to significantly extend the maximum 12,742 km (7,918 miles) baseline of the terrestrial EHT array and provide a capability to image the photon ring in greater detail.

Here’s how the EHT terrestrial baseline would change with space-based observatories:

  • Low Earth orbit (LEO):  Add 370 – 460 km (230 – 286 miles) for a single telescope in an orbit similar to the International Space Station
  • Geosynchronous orbit: Add 35,786 km (22,236 mi) for a single telescope, or up to twice that for multiple telescopes
  • Moon: Add Earth-Moon average distance: 384,472 km (238,900 miles)
  • L2 Lagrange point: Add about 1.5 million km (932,057 miles)

It seems to me that several EHT observatories in geosynchronous orbits could be a good solution that could be implemented sooner than an observatory on the Moon or at L2.  Geosynchronous telescopes would greatly expand the EHT baseline and the spacecraft could make long observing runs from orbital positions that are relatively fixed in relation to the terrestrial EHT sites.  In-orbit servicing would be more practical in geosynchronous orbit than at L2.  In February 2020, Northrop-Grumman demonstrated the ability to remotely restore a large communications satellite that was running out of fuel in geosynchronous orbit.  With remote servicing, a geosynchronous observatory could have a long operating life.

6. In conclusion:

With the ongoing improvements to the terrestrial EHT array and its data recording and processing systems, we should see many more black hole observations reported in the years ahead.  I’m looking forward to direct observation of M87’s photon ring and the first look at the Sagittarius A* black hole near the center of our Milky Way galaxy.  The time delay between data acquisition (i.e., from a series of observation runs of a particular target) and reporting is about three years. This is understandable given the mass of data that must be aggregated from the many EHT observatories to synthesize images of a target black hole.  Hopefully, this time delay can be shortened in the years ahead. 

Within the next decade, a plan to expand the EHT array to include orbital and/or lunar observatories could be in developed.  Hopefully, funding for spacecraft development and deployment will follow.

7. For more information:

See the following sources for more information on the EHT and imaging a black hole:

A Third Source of Gravitational Waves Appears to Have Been Detected

Peter Lobner

The US Laser Interferometer Gravitational-Wave Observatory (LIGO) began its third “observing run,” O3, on 1 April 2019 after a series of upgrades were completed on both LIGO instruments (in Hanford, Washington and Livingston, Louisiana) during an 18-month shutdown period after the second observing run, O2, ended on 25 August 2017.  The European Gravitational Observatory’s (EGO) Virgo instrument also joined O3.  Since its last observing run, which coincided with part of LIGO O2, Virgo also received a series of upgrades that have almost doubled its sensitivity.  O3 is scheduled to last for one calendar year.  Check out the details of these gravitational wave instruments and O3 at the following websites:

On 12 August, the LIGO / Virgo team reported:

“By July 31st, 2019, LIGO had sent out 25 alerts to possible detections, three have since been retracted, leaving us with 22 ‘candidate’ gravitational wave events. We call them “candidates” because we still need time to vet all of them. If all candidates are verified, then the number of detections made by LIGO in just the first third of O3 will double the number of detections made in its first two runs combined……So far, no electromagnetic counterparts related to our public alerts have been observed, but all candidates are being actively analyzed by LSC/Virgo science teams.”

As of July 31, 2019 LIGO/Virgo had seen:

  • 18 binary black hole merger candidates
  • 4 binary neutron star merger candidates

The LIGO-Virgo Collaboration has created the Gravitational Wave Candidate Event Database (GraceDB), which members of the public can access to track observations made during O3 here: 

https://gracedb.ligo.org/superevents/public/O3/

On 14 August 2019, the LIGO and Virgo instruments detected a gravitational wave event that appears to have come from a previously undetected source: the collision of a black hole and a neutron star.  This event, tentatively identified as S190814bv, is estimated to have occurred about 900 million light-years away.   Data from the three detectors enabled scientists to locate the source of these gravitational waves to a 23 square degree region of the sky, which would be about seven times the diameter of the Moon as seen from Earth.  While the gravitational wave signal was characterized as “remarkably strong,” so far, there have been no “multi-messenger” detections in the electromagnetic spectrum to help further refine the location and the nature of the event.

You’ll find a description of a black hole collision with a neutron star on the Simulating eXtreme Spacetimes (SXS) website at the following link:

https://www.black-holes.org/the-science-compact-objects/compact-objects/black-holes-and-neutron-stars

Here, SXS offers the following sequence of events for this exotic collision. 

Neutron star beginning to disrupt. The tidal forces of the black hole squeeze the star like a tube of toothpaste. The distance between the neutron star and the black hole is about 50 km, and they are orbiting hundreds of times per second. Source: SXS
Ejected tail flinging off into space. This matter will eventually contribute rare heavy elements to the interstellar medium. Source: SXS
Accretion disk swirling around the black hole. The accretion disk survives outside the black hole for less than a second. But this is enough time to release an enormous amount of energy in the form of neutrinos. It spans a little more than a hundred km from side to side.
Source: SXS

For more information, check the LIGO and Virgo websites for their news updates.

The Event Horizon Telescope Team has Produced the First Image Showing the Shadow of a Black Hole

Updated 7 April 2020

Peter Lobner

The first image of a black hole was released on 10 April 2019  at a press conference in Washington D.C. held by the Event Horizon Telescope (EHT) team and the National Science Foundation (NSF).  The subject of the image is the supermassive black hole located near the center of the Messier 87 (M87) galaxy.  This black hole is about 55 million light years from Earth and is estimated to have a mass 6.5 billion times greater than our Sun.  The image shows a glowing circular emission ring surrounding the dark region (shadow) containing the black hole.  The brightest part of the image also may have captured a bright relativistic jet of plasma that appears to be streaming away from the black hole at nearly the speed of light, beaming generally in the direction of Earth.

The first ever image showing the shadow of a black hole (M87), which remains unseen at the center of the dark circular region.
Source:The EHT Collaboration, et al.

The EHT is not one physical telescope.  Rather, it an array of millimeter and sub-millimeter wavelength radio telescopes located around the world.  The following map shows the eight telescopes that participated in the 2017 observations of M87.  Three additional telescopes joined the EHT array in 2018 and later.  

The EHT array as used for the April 2017 observations.  
Source: The EHT Collaboration, et al.

All of the EHT telescopes are used on a non-dedicated basis by an EHT team of more than 200 researchers during a limited annual observing cycle.  The image of the M87 black hole was created from observations made during a one week period in April 2017.

The long baselines between the individual radio telescopes give the “synthetic” EHT the resolving power of a physical radio telescope with a diameter that is approximately equal to the diameter of the Earth. A technique called very long-baseline interferometry (VLBI) is used to combine the data from the individual telescopes to synthesize the image of a black hole. EHT Director, Shep Doeleman, referred to VLBI as “the ultimate in delayed gratification among astronomers.” The magnifying power of the EHT becomes real only when the data from all of the telescopes are brought together and the data are properly combined and processed. This takes time.

At a nominal operating wavelength of about 1.3 mm (frequency of 230 GHz), EHT angular resolution is about 25 microarcseconds (μas), which is sufficient to resolve nearby supermassive black hole candidates on scales that correspond to their event horizons.  The EHT team reports that the M87 bright emission disk subtends an angle of 42 ± 3 microarcseconds.

For comparison, the resolution of a human eye in visible light is about 60 arcseconds (1/60thof a degree; there are 3,600 arcseconds in one degree) and the 2.4-meter diameter Hubble Space Telescope has a resolution of about 0.05 arcseconds (50,000 microarcseconds).

You can read five open access papers on the first M87 Event Horizon Telescope results written by the EHT team and published on 10 April 2019 in the Astrophysical Journal Letters here:

Congratulations to the EHT Collaboration for their extraordinary success in creating the first-ever image of a black hole shadow.

7 April 2020 Update:  EHT observations were complemented by multi-spectral (multi-messenger) observations by NASA spacecraft

On 10 April 2019, NASA reported on its use of several orbiting spacecraft to observe M87 in different wavelengths during the period of the EHT observation.

  • “To complement the EHT findings, several NASA spacecraft were part of a large effort, coordinated by the EHT’s Multiwavelength Working Group, to observe the black hole using different wavelengths of light. As part of this effort, NASA’s Chandra X-ray Observatory, Nuclear Spectroscopic Telescope Array (NuSTAR) and Neil Gehrels Swift Observatory space telescope missions, all attuned to different varieties of X-ray light, turned their gaze to the M87 black hole around the same time as the EHT in April 2017. NASA’s Fermi Gamma-ray Space Telescope was also watching for changes in gamma-ray light from M87 during the EHT observations.”
  • “NASA space telescopes have previously studied a jet extending more than 1,000 light-years away from the center of M87. The jet is made of particles traveling near the speed of light, shooting out at high energies from close to the event horizon. The EHT was designed in part to study the origin of this jet and others like it.”

NASA’s Neutron star Interior Composition Explorer (NICER) experiment on the International Space Station also contributed to the multi-spectral observations of M87, which were coordinated by EHT’s Multiwavelength Working Group.

Chandra X-ray Observatory close-up of the core of the M87 galaxy,
showing the location of the black hole (+) and the relativistic jet.
Source: NASA/CXC/Villanova University/J. Neilsen

On April 25, 2019, NASA released the following composite image showing the M87 galaxy, the position of the black hole and large relativistic jets of matter being ejected from the black hole.  These infrared images were made by NASA’s orbiting Spitzer Space Telescope.  

The M87 galaxy, with two expanded views, first showing the location of the black hole and two plasma jets (orange) at the center of M87, and second, the closeup EHT image of the black hole’s shadow.  
Source: NASA/JPL-Caltech/IPAC/Event Horizon Telescope

For more information:

See the following sources for more information on the EHT and imaging the M87 black hole:

Standby for a New Round of Gravitational Wave Detection

Peter Lobner

Since late August 2017, the US LIGO 0bservatories in Washington and Louisiana and the European Gravitational Observatory (EGO), Virgo, in Italy, have been off-line for updating and testing.  These gravitational wave observatories were set to start Observing Run 3 (O3) on 1 April 2019 and conduct continuous observations for one year.  All three of these gravitational wave observatories have improved sensitivities and are capable of “seeing” a larger volume of the universe than in Observing Run 2 (O2).

Later in 2019, the Japanese gravitational wave observatory, KAGRA, is expected to come online for the first time and join O3.  By 2024, a new gravitational wave observatory in India is expected to join the worldwide network.

On the advent of this next gravitational wave detection cycle, here’s is a brief summary of the status of worldwide gravitational wave observatories.

Advanced LIGO 

The following upgrades were implemented at the two LIGO observatories since Observing Run 2 (O2) concluded in 2017:

  • Laser power has been doubled, increasing the detectors’ sensitivity to gravitational waves.
  • Upgrades were made to LIGO’s mirrors at both locations, with five of eight mirrors being swapped out for better-performing versions.
  • Upgrades have been implemented to reduce levels of quantum noise. Quantum noise occurs due to random fluctuations of photons, which can lead to uncertainty in the measurements and can mask faint gravitational wave signals. By employing a technique called quantum “squeezing” (vacuum squeezing), researchers can shift the uncertainty in the laser light photons around, making their amplitudes less certain and their phases, or timing, more certain. The timing of photons is what is crucial for LIGO’s ability to detect gravitational waves.  This technique initially was developed for gravitational wave detectors at the Australian National University, and matured and routinely used since 2010 at the GEO600 gravitational wave detector in Hannover, Germany,

In comparison to its capabilities in 2017 during O2, the twin LIGO detectors have a combined increase in sensitivity of about 40%, more than doubling the volume of the observable universe.

You’ll find more news and information on the LIGO website at the following link:

https://www.ligo.caltech.edu/news

GEO600 

GEO600 is a modest-size laser interferometric gravitational wave detector (600 meter / 1,969 foot arms) located near Hannover, Germany. It was designed and is operated by the Max Planck Institute for Gravitational Physics, along with partners in the United Kingdom.

In mid-2010, GEO600 became the first gravitational wave detector to employ quantum “squeezing” (vacuum squeezing) and has since been testing it under operating conditions using two lasers: its standard laser, and a “squeezed-light” laser that just adds a few entangled photons per second but significantly improves the sensitivity of GEO600.  In a May 2013 paper entitled, “First Long-Term Application of Squeezed States of Light in a Gravitational Wave Observatory,” researchers reported the following results of operational tests in 2011 and 2012.

“During this time, squeezed vacuum was applied for 90.2% (205.2 days total) of the time that science-quality data were acquired with GEO600. A sensitivity increase from squeezed vacuum application was observed broadband above 400 Hz. The time average of gain in sensitivity was 26% (2.0 dB), determined in the frequency band from 3.7 to 4.0 kHz. This corresponds to a factor of 2 increase in the observed volume of the Universe for sources in the kHz region (e.g., supernovae, magnetars).”

The installed GEO600 squeezer (in the foreground) inside the GEO600 clean room together with the vacuum tanks (in the background).  
Source: http://www.geo600.org/15581/1-High-Tech

While GEO600 has conducted observations in coordination with LIGO and Virgo, GEO600 has not reported detecting gravitational waves. At high frequencies GEO600 sensitivity is limited by the available laser power. At the low frequency end, the sensitivity is limited by seismic ground motion.

You’ll find more information on GEO600 at the following link:

http://www.geo600.org/3020/About-GEO600

Advanced Virgo, the European Gravitational Observatory (EGO)

At Virgo, the following upgrades were implemented since Observing Run 2 (O2) concluded in 2017:

  • The steel wires used during O2 observation campaign to suspend the four main mirrors of the interferometer have been replaced.  The 42 kg (92.6 pound) mirrors now are suspended with thin fused-silica (glass) fibers, which are expected to increase the sensitivity in the low-medium frequency region.  The mirrors in Advanced LIGO have been suspended by similar fused-silica fibers since those two observatories went online in 2015.
  • A more powerful laser source has been installed, which should improve sensitivity at high frequencies. 
  • Quantum “squeezing” has been implemented in collaboration with the Albert Einstein Institute in Hannover, Germany.  This should improve the sensitivity at high frequencies.
Virgo mirror suspension with fused-silica fibers.  
Source: EGO/Virgo Collaboration/Perciballi

In comparison to its capabilities in 2017 during O2, Virgo sensitivity has been improved by a factor of about 2, increasing the volume of the observable universe by a factor of about 8.

You’ll find more information on Virgo at the following link:

http://www.virgo-gw.eu

Japan’s KAGRA 

KAGRA is a cryogenically-cooled laser interferometer gravitational wave detector that is sited in a deep underground cavern in Kamioka, Japan.  This gravitational wave observatory is being developed by the Institute for Cosmic Ray Research (ICRR) of the University of Tokyo.  The project website is at the following link:

https://gwcenter.icrr.u-tokyo.ac.jp/en/

One leg of the KAGRA interferometer.  
Source: ICRR, University of Tokyo

The cryogenic mirror cooling system is intended to cool the mirror surfaces to about 20° Kelvin (–253° Celsius) to minimize the motion of molecules (jitter) on the mirror surface and improve measurement sensitivity.   KAGRA’s deep underground site is expected to be “quieter” than the LIGO and VIRGO sites, which are on the surface and have experienced effects from nearby vehicles, weather and some animals.

The focus of work in 2018 was on pre-operational testing and commissioning of various systems and equipment at the KAGRA observatory. In December 2018, the KAGRA Scientific Congress reported that, “If our schedule is kept, we expect to join (LIGO and VIRGO in) the latter half of O3…”   You can follow the latest news from the KAGRA team here:

https://gwcenter.icrr.u-tokyo.ac.jp/en/category/latestnews

LIGO-India

IndIGO, the Indian Initiative in Gravitational-wave Observations, describes itself as an initiative to set up advanced experimental facilities, with appropriate theoretical and computational support, for a multi-institutional Indian national project in gravitational wave astronomy.  The IndIGO website provides a good overview of the status of efforts to deploy a gravitational wave detector in India.  Here’s the link:

http://www.gw-indigo.org/tiki-index.php?page=Welcome

On 22 January 2019, T. V. Padma reported on the Naturewebsite that India’s government had given “in-principle” approval for a LIGO gravitational wave observatory to be built in the western India state of Maharashtra. 

“India’s Department of Atomic Energy and its Department of Science and Technology signed a memorandum of understanding with the US National Science Foundation for the LIGO project in March 2016. Under the agreement, the LIGO Laboratory — which is operated by the California Institute of Technology (Caltech) in Pasadena and the Massachusetts Institute of Technology (MIT) in Cambridge — will provide the hardware for a complete LIGO interferometer in India, technical data on its design, as well as training and assistance with installation and commissioning for the supporting infrastructure. India will provide the site, the vacuum system and other infrastructure required to house and operate the interferometer — as well as all labor, materials and supplies for installation.”

India’s LIGO observatory is expected to cost about US$177 million.  Full funding is expected in 2020 and the observatory currently is planned for completion in 2024.  India’s Inter-University Centre for Astronomy and Astrophysics (IUCAA), also in Maharashtra  state, will lead the project’s gravitational-wave science and the new detector’s data analysis.

For T. V. Padma’s complete article, refer to: 

https://www.nature.com/articles/d41586-019-00184-z.

Spatial resolution of gravitational wave events

Using only the two US LIGO detectors, it is not possible to localize the source of gravitational waves beyond a broad sweep through the sky.  On 1 August 2017, Virgo joined LIGO during the second Observation Run, O2. While the LIGO-Virgo three-detector network was operational for only three-and-a-half weeks, five gravitational wave events were observed.  As shown in the following figure, the spatial resolution of the source was greatly improved when a triple detection was made by the two LIGO observatories and Virgo. These events are labeled with the suffix “HLV”.  

Source:  http://www.virgo-gw.eu, 3 December 2018

The greatly reduced areas of the triple event localizations demonstrate the capabilities of the current global gravitational wave observatory network to resolve the source of a gravitational-wave detection.  The LIGO and Virgo Collaboration reports that it can send Open Public Alerts within five minutes of a gravitational wave detection.

With timely notification and more precise source location information, other land-based and space observatories can collaborate more rapidly and develop a comprehensive, multi-spectral (“multi-messenger”) view of the source of the gravitational waves.

When KAGRA and LIGO-India join the worldwide gravitational wave detection network, it is expected that source localizations will become 5 to 10 times more accurate than can be accomplished with just the LIGO and Virgo detectors.

For more background information on gravitational-wave detection, see the following Lyncean posts:

Visitors From Outside our Solar System May be More Common Than We Expected

Peter Lobner

No!  This is not a story about UFOs.  On 19 October 2017, astronomers using the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1)in Hawaii made the first detection of an interstellar object passing through our solar system.  PanSTARRS 1 uses a Moving Object Processing System (MOPS) that is designed to detect fast moving objects in the vicinity of the Earth as well as those moving as slowly as the fastest proper motion stars.  The original goal of  the PanSTARRS project, which began observations in 2007, was to detect objects 100 times fainter than previous sky surveys, including 99% of the asteroids 300 meters (1,309 feet) or larger that come near Earth’s orbit.

NASA reported: “Rob Weryk, a postdoctoral researcher at the University of Hawaii Institute for Astronomy, was first to identify the moving object and submit it to the Minor Planet Center. Weryk subsequently searched the Pan-STARRS image archive and found it also was in images taken the previous night, but was not initially identified by the moving object processing.”

Pan-STARRS1 on Haleakala, Hawaii.  Source: https://panstarrs.stsci.edu

You’ll find a description of PanSTARRS 1 here;

https://panstarrs.stsci.edu/attachments/metcalfe_nam2015.pdf

The PanSTARRS1 MOPS is described in more detail here.

https://amostech.com/TechnicalPapers/2009/Astronomy/Denneau.pdf

The interstellar object discovered by Pan-STARRS1 was designated Asteroid  1I/2017 U1, and later was named Oumuamua, which means “a messenger from afar arriving first” in Hawaiian.  The red-hued object has a highly-elongated  shape (cigar-shaped) with a length of about a quarter mile (1,320 feet, 402 meters) and a diameter of  about 120 feet (40 meters).  Oumuamua was unlike any asteroid or comet previously observed in our solar system.

Artist’s concept of  Oumuamua. Source: European Southern Observatory/M. Kornmesser

Before its detection by PanSTARRS1, Oumuamua had entered our solar system and made its closest approach to the Sun on 19 September 2017, reaching a speed of about 196,000 mph (315,400 km/h).  From analysis of its trajectory, astronomers determined that Oumuamua most likely came from outside our solar system.  On its outbound trajectory, it was moving fast enough to escape the Sun’s gravitational field and break free of the solar system, never to return.

Oumuamua’s trajectory through our solar system. Source: NASA/JPL-Caltech

You’ll find a NASA/JPL-Caltech animation of Oumuamua’s trajectory here:

https://www.nasa.gov/feature/jpl/small-asteroid-or-comet-visits-from-beyond-the-solar-system

The European Space Agency (ESA) reported the following:

  • Oumuamua is dense, possibly rocky or with high metal content, lacks significant amounts of water or ice, and that its surface is now dark and reddened due to the effects of irradiation from cosmic rays over millions of years….it is completely inert, without the faintest hint of dust around it.
  • Preliminary orbital calculations suggested that the object had come from the approximate direction of the bright star Vega, in the northern constellation of Lyra. However, even travelling at a breakneck speed of about 95,000 kilometers/hour (59,000 mph), it took so long for the interstellar object to make the journey to our Solar System that Vega was not near that position when the asteroid was there about 300,000 years ago. Oumuamua may well have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with the Solar System.

You can read the ESA report here:

https://www.eso.org/public/news/eso1737/

The Breakthrough Listen initiative reported that the Green Bank Telescope in West Virginia detected no evidence of artificial signals emanating from the object.

To the disappointment of science fiction fans, all observations were consistent with Oumuamua being a natural object, and not a derelict spaceship, like the Battlestar Galactica.

Source: https://abagond.wordpress.com/2017/11/25/oumuamua/

David  Clery’s 21 May 2018 article, “This asteroid came from another solar system—and it’s here to stay,” describes the 2014 discovery and recent analysis of an object in our solar that is in a retrograde, heliocentric orbit at approximately the distance of Jupiter from the Sun (483.8 million miles / 778.6 million km).  The asteroid, identified as 2015 BZ509, is traveling around our solar system in the opposite directions of almost everything else in an orbit with unusual elongation and inclination to the plane of the solar system.  The recent analysis indicates that this is a stable orbit, and not a fly-by trajectory through our solar system like the brief visit of Oumuamua.

You can read David Clery’s article on the Science website here:

http://www.sciencemag.org/news/2018/05/asteroid-came-another-solar-system-and-it-s-here-stay?utm_campaign=news_daily_2018-05-21&et_rid=215579562&et_cid=2065701

The original paper by F. Namouni and M H M Morais, “An interstellar origin for Jupiter’s retrograde co-orbital asteroid,”was published on 21 May 2018 in the Monthly Notices of the Royal Astronomical Society.  The paper describes the analysis of the orbital parameters that that led to the conclusion the asteroid 2015 BZ509 was in a stable orbit.  The authors reported:

“Asteroid (514107) 2015 BZ509 was discovered recently in Jupiter’s co-orbital region with a retrograde motion around the Sun. The known chaotic dynamics of the outer Solar system have so far precluded the identification of its origin. Here, we perform a high-resolution statistical search for stable orbits and show that asteroid (514107) 2015 BZ509 has been in its current orbital state since the formation of the Solar system. This result indicates that (514107) 2015 BZ509 was captured from the interstellar medium 4.5 billion years in the past as planet formation models cannot produce such a primordial large-inclination orbit with the planets on nearly coplanar orbits interacting with a coplanar debris disc that must produce the low-inclination small-body reservoirs of the Solar system such as the asteroid and Kuiper belts. This result also implies that more extrasolar asteroids are currently present in the Solar system on nearly polar orbits.”

You can read the full paper here.

https://academic.oup.com/mnrasl/article/477/1/L117/4996014

Source: Screenshot from animation of 2015 BZ509 orbit created by the Large Binocular Telescope Observatory

You can view a short animation created by the Large Binocular Telescope Observatory to illustrate the dynamics of the unusual retrograde orbit of 2015 BZ509 here.

https://www.youtube.com/watch?v=7_QbYX4jTrI

It’s an intriguing prospect that there are more extrasolar objects in stable orbits around our Sun.  Could one of them be the elusive Planet 9?  For an update on the search for Planet 9, see the 21 May 2018 article by Elizabeth Howell, “Weird Space Rock Provides More Evidence for Mysterious ‘Planet Nine’,” which is on the Space.com website at the following link:

https://www.space.com/40642-space-rock-generates-planet-nine-excitement.html

The potential orbit of Planet 9, illustrated with the existing orbit of several trans-Neptunian objects (TNOs).Source: R. Hurt/JPL-Caltech

Gravitational Waves Come in Colors

Peter Lobner

On 14 September 2015, the Laser Interferometer Gravitational-Wave Observatory (LIGO) ushered in a new era in astronomy and astrophysics by opening a part of the gravitational wave spectrum to direct observation. In my 17 February 2017 post,“Perspective on the Detection of Gravitational Waves,” I included the following graphic from an interview of Kip Thorne by Walter Issacson.

Source: screenshot from Kip Thorne / Walter Issacson interview at: https://www.youtube.com/watch?v=mDFF27Nr-EU

The key point of this graphic is to illustrate how the LIGO detector is able to “see” only a part of the gravitational wave spectrum.  The LIGO team reported that the Advanced LIGO detector is optimized for “a range of frequencies from 30 Hz to several kHz, which covers the frequencies of gravitational waves emitted during the late inspiral, merger, and ringdown of stellar-mass binary black holes.”  This is the type of event associated with the first several gravitational wave detections. The European Advanced VIRGO detector, which came on line in 2017, operates on the same principle as LIGO, precisely measuring differences in the times-of-flight of laser beams in the two legs of a long baseline interferometer. VIRGO is optimized to view a range of gravitational wave frequencies from about 10 Hz to 10 kHz.

On 17 August 2017, LIGO and VIRGO detected gravitational waves from a different source: the collision of two neutron stars. Unlike the previous gravitational wave detections from black hole coalescence, the neutron star collision that produced GW180817 also produced other observable phenomena in multiple wavelength bands. LIGO and VIRGO triangulated the source of this gravitational wave event, which also was observed by dozens of telescopes on the ground and in space, as shown in the following diagram.

Source: LIGO – VIRGO, https://www.ligo.org/detections/GW170817/images-GW170817/GW+EM_Observatories.jpg

The ability to cue a worldwide array of multi-spectral observatories on short notice greatly added to the depth of understanding of the GW170817 event.  The international collaboration on this event was a great example of the benefits of “multi-messenger” astronomy. For more information, see my 25 October 2017 post, “Linking Gravitational Wave Detection to the Rest of the Observable Spectrum.”

At the 11 April 2018 Lyncean Group meeting, Dr. Rana Adhikari, Professor of Physics, Mathematics and Astronomy at Caltech, provided an update on LIGO in his presentation, “The Dirty Details of Detecting Gravitational Waves from Black Holes.” You can view Dr. Adhikari’s presentation slides at the following link:

https://lynceans.org/talk-119-4-11-18/

As we have seen, the LIGO class of gravitational wave detector is capable of seeing large amplitude, relatively high frequency gravitational waves from very powerful, discrete events: stellar-mass binary black hole coalescence and neutron star collisions.

As shown in the above graphic, viewing lower frequency (longer wavelength) gravitational waves requires different types of detectors, which are discussed below.

LISA –  Laser Interferometer Space Antenna

This will be a very long baseline, equilateral triangular laser interferometer in space, established of three spacecraft flying in formation in an Earth-trailing heliocentric orbit.  Each leg of the space interferometer will measure 2.5 million kilometers (1.55 million miles), about 625,000 times the length of the LIGO baseline (4 km, 2.49 miles). Each spacecraft will contain a gravitational wave detector sensitive at frequencies from about 10-4 Hz to 10-1 Hz, well below the frequency range of LIGO and VIRGO.

The European Space Agency’s (ESA) LISA Pathfinder spacecraft, which was launched in 2015 and ended its mission in July 2017, validated the technology for the LISA space interferometer.

Source: ESA, https://www.elisascience.org/

ESA reported:

“Analysis of the LISA Pathfinder mission results towards the end of the mission (red line) compared with the first results published shortly after the spacecraft began science operations (blue line). The initial requirements (top, wedge-shaped area) and that of the future gravitational-wave observatory LISA (middle, striped area) are included for comparison, and show that LISA Pathfinder far exceeded expectations.”

The ESA is planning to launch LISA in the 2029 – 2032 timeframe.  See my 27 September 2016 post, “Space-based Gravity Wave Detection System to be Deployed by ESA,” for additional information on LISA.  The LISA mission website is at the following link:

https://www.elisascience.org

PTA – Pulsar Timing Array

A pulsar is a highly magnetized rotating neutron star or white dwarf that emits a beam of electromagnetic radiation. This radiation can be observed only when the beam is pointing toward Earth.

PTA gravitational wave detection is based on correlated radio-telescope observations of an array of many pulsars known as “millisecond pulsars” (MSPs).  The signal from an MSP has a very predictable time-of-arrival (TOA), thereby allowing each MSP to function as a galactic “clock.”  Small disturbances in each “clock” are measurable with high precision on Earth.  In essence, the distance between an MSP and the observing radio-telescope forms one leg of a gravitational wave detector, with the leg length being measured in light-years.  A disturbance from a passing gravitational wave would to have a measurable signature across the many MSPs in the pulsar timing array.

A PTA is intended to observe in a different range in gravitational wave frequencies than LIGO and VIRGO, and is expected to see a different category of gravitational wave sources. Whereas LIGO and VIRGO can detect gravitational waves in the tens to thousands of Hz (audio) range, radio-telescope observatories currently are using PTAs to search for gravitational waves in the tens to hundreds of microHertz (10-6Hz) range with prospects of getting down to the 10-8Hz range. The primary source of gravitational waves in this frequency range is expected to be super-massive black hole binaries (billions of solar masses), which are believed to exist throughout the universe at the center of galaxies.

The International Pulsar Timing Array (IPTA) is an international collaboration among the following radio-telescope consortia: European Pulsar Timing Array (EPTA), the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), and the Parkes Pulsar Timing Array (PPTA).  The goal of the IPTA is to detect gravitational waves using an array of about 30 MSPs. IPTA reports:

“Using telescopes located around the world is important, because any single telescope can see (a particular) pulsar … for much less than twelve hours, depending on the observing site’s latitude. Thus, the telescopes “trade off” between one another – as the pulsar sets from the perspective of, say, the Parkes telescope in Australia, it rises from the perspective of the Lovell telescope in the UK.”

You’ll find more information on IPTA on their website at the following link:

http://www.ipta4gw.org

You can visit the NANOGrav website here:

http://nanograv.org

Continuous gravitational waves

On 10 April 2018, the Max Planck Institute for Gravitational Physics announced the formation of a permanent Max Planck Independent Research Group under the leadership of Dr. M. Alessandra Papa to search for continuous gravitational waves.  The primary goal of this research group is to make the first direct detection of gravitational waves from rapidly rotating neutron stars. You can read this announcement here:

http://www.aei.mpg.de/2236875/searchingcontinuouswaves

Generation of the weak, continuous gravitational waves depends on the neutron star having an asymmetry that would perturb the stars gravitational field as it rapidly rotates. The method for detecting these weak, continuous gravitational waves was not described in the Planck Institute announcement.

CMB – Cosmic microwave background

The CBM is believed to be an artifact of the Big Bang and could carry evidence of the primordial gravitational waves from that era.  Such evidence would be expected to stretch across broad areas of the observable universe.

The European Space Agency (ESA) developed the Planck space observatory to map the CMB in microwave and infrared frequencies at unprecedented levels of detail. The Planck spacecraft was launched on 14 May 2009 and operated until 23 October 2013.  In 2016, the ESA released the results of the Planck all-sky survey of the CBM, which revealed that the universe appears to be isotropic, at least at the resolution of the Planck space observatory.  Researchers found that the actual CMB shows only random noise and no signs of patterns.

Planck all-sky survey. Source; ESA / Planck Collaboration

You’ll find more information on the Planck mission in my 28 September 2016 post, “The Universe is Isotropic.”

You can access ESA’s Planck science team home page here:

https://www.cosmos.esa.int/web/planck/home

In summary

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) website contains the following summary chart, which is an alternate view of the chart at the start of this article (from the Kip Thorne / Walter Issacson interview).  The NANOGrav chart provides a good perspective on the observational technologies that are opening windows into the broad spectrum of gravitational waves and their varied sources.

So, in an analogy to the optical spectrum and the range of colors we see every day, the primordial gravitational waves in the CBM would be at the “red” end of the gravitational wave spectrum. The much higher frequency gravitational waves seen by LIGO and VIRGO, from stellar-mass binary black hole coalescence and neutron star collisions, would be at the “violet” end of the gravitational wave spectrum. The LISA space-based interferometer will be looking in the “blue-green” range, while PTA observatories are looking in the “yellow-orange” range.

For more information on the current state of gravitational wave technology, you’ll find a good survey article by Davide Castelvecchia, entitled “Here Come the Waves,” in the 12 April 2018 issue of Nature, which you can read here:

https://www.nature.com/magazine-assets/d41586-018-04157-6/d41586-018-04157-6.pdf