SCIENCE

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A GLIMPSE AT THE CHAOS OF A BLACK HOLE

Photo Credit - Event Horizon Telescope collaboration et al


NASA  - A black hole and its shadow have been captured in an image for the  first time, a historic feat by an international network of radio  telescopes called the Event Horizon Telescope (EHT). EHT is an  international collaboration whose support in the U.S. includes the  National Science Foundation.


A  black hole is an extremely dense object from which no light can escape.  Anything that comes within a black hole’s “event horizon,” its point of  no return, will be consumed, never to re-emerge, because of the black  hole’s unimaginably strong gravity. By its very nature, a black hole  cannot be seen, but the hot disk of material that encircles it shines  bright. Against a bright backdrop, such as this disk, a black hole  appears to cast a shadow.


The  stunning new image shows the shadow of the supermassive black hole in  the center of Messier 87 (M87), an elliptical galaxy some 55 million  light-years from Earth. This black hole is 6.5 billion times the mass of  the Sun. Catching its shadow involved eight ground-based radio  telescopes around the globe, operating together as if they were one  telescope the size of our entire planet.


“This  is an amazing accomplishment by the EHT team,” said Paul Hertz,  director of the astrophysics division at NASA Headquarters in  Washington. “Years ago, we thought we would have to build a very large  space telescope to image a black hole. By getting radio telescopes  around the world to work in concert like one instrument, the EHT team  achieved this, decades ahead of time.”


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  Event Horizon Telescope in April 2017. If EHT observed changes in the  structure of the black hole’s environment, data from these missions and  other telescopes could be used to help figure out what was going on.


While  NASA observations did not directly trace out the historic image,  astronomers used data from NASA’s Chandra and NuSTAR satellites to  measure the X-ray brightness of M87’s jet. Scientists used this  information to compare their models of the jet and disk around the black  hole with the EHT observations. Other insights may come as researchers  continue to pore over these data.


There  are many remaining questions about black holes that the coordinated  NASA observations may help answer. Mysteries linger about why particles  get such a huge energy boost around black holes, forming dramatic jets  that surge away from the poles of black holes at nearly the speed of  light. When material falls into the black hole, where does the energy  go?


“X-rays  help us connect what’s happening to the particles near the event  horizon with what we can measure with our telescopes,” said Joey  Neilsen, an astronomer at Villanova University in Pennsylvania, who led  the Chandra and NuSTAR analysis on behalf of the EHT’s Multiwavelength  Working Group.


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. A blob of matter in  the jet called HST-1, discovered by Hubble astronomers in 1999, has  undergone a mysterious cycle of brightening and dimming.


Chandra,  NuSTAR and Swift, as well as NASA’s Neutron star Interior Composition  Explorer (NICER) experiment on the International Space Station, also  looked at the black hole at the center of our own Milky Way galaxy,  called Sagittarius A*, in coordination with EHT.


Getting  so many different telescopes on the ground and in space to all look  toward the same celestial object is a huge undertaking in and of itself,  scientists emphasize.


“Scheduling  all of these coordinated observations was a really hard problem for  both the EHT and the Chandra and NuSTAR mission planners,” Neilsen said.  “They did really incredible work to get us the data that we have, and  we’re exceedingly grateful.”



Neilsen  and colleagues who were part of the coordinated observations will be  working on dissecting the entire spectrum of light coming from the M87  black hole, all the way from low-energy radio waves to high-energy gamma  rays. With so much data from EHT and other telescopes, scientists may  have years of discoveries ahead.