The first direct visual evidence of a black hole and its “shadow” has been revealed today by astronomers working on the Event Horizon Telescope (EHT). The image is of the supermassive black hole that lies at the centre of the huge Messier 87 galaxy, in the Virgo galaxy cluster. Located 55 million light-years from Earth, the black hole has been determined to have a mass 6.5 billion times that of the Sun, with an uncertainty of 0.7 billion solar masses. Although black holes are inherently invisible because of their extreme density and gravitational field, the researchers have managed to obtain images near the point where matter and energy can no longer escape – the so-called event horizon.
“We are giving humanity its first view of a black hole — a one-way door out of our universe,” says Sheperd Doeleman of the Haystack Observatory at the Massachusetts Institute of Technology (MIT) who is the EHT’s lead astronomer. “This is a landmark in astronomy, an unprecedented scientific feat accomplished by a team of more than 200 researchers.” Doeleman says that the result would have been “presumed to be impossible just a generation ago”, adding that breakthroughs in technology and the completion of new radio telescopes over the past decade have allowed researchers to now “see the unseeable”.
Discs of glowing gas
Supermassive black holes are thought to lie at the centres of most galaxies in the universe, and astronomers are keen to decipher their key properties – such as how their extreme gravity affects the space–time around them, and how some of them fuel the massive jets of material that spew out from the galaxies that host them. A key feature of a black hole is its event horizon – the boundary at which even light cannot escape its gravitational pull, as the velocity required to do so would be greater than the speed of light, which is forbidden by Einstein’s general theory of relativity. And while that theory has passed many tests, researchers want to see how well it holds up at the “ultimate proving ground” – a black hole’s edge.
Despite their name, black holes are not, however, all dark. The gas and dust trapped around them in an accretion disc is so compact that it is often heated to billions of degrees even before the matter eventually succumbs to the black hole, making them glow brightly. Indeed, general relativity also predicts that a black hole will have a “shadow” around it, measuring around three times larger than the event horizon. The shadow is of great interest as its size and shape depend mainly on the mass and – to a lesser extent – on any possible spin of the black hole, thereby revealing its inherent properties.
Where is it located?
It is located at the center of Messier 87 Galaxy.
The massive galaxy M87 is the most spectacular example of an elliptical galaxy we can see from Earth. The most fascinating feature of this galaxy is its jet, which is visible in optical light as well as x-rays and radio emissions.
The jet extends from the central supermassive black hole of the galaxy and reaches out about 5,000 light-years. As a true elliptical galaxy, M87 has no obvious dust lanes and very little evidence of star formation. It likely formed from a recent merger between two other galaxies.
Facts about M87
- The interstellar medium in M87 is filled with gas that has been enriched somewhat by materials from stars that died long ago. There is dust in the galaxy, but far less than the Milky Way contains.
- The black hole at M87’s heart has the mass of about 3.5 billion Suns. It is surrounded by a disk of material that is slowly funneling into the black hole, heated by the action of a jet that is moving at very high speed out from the black hole.
- It is possible that the core of M87 has more than one supermassive black hole.
- The nuclear region of M87 is known as an “active galactic nucleus” due to its brightness in visible, x-ray, radio, and other wavelengths of light.
- M87 is surrounded by a corona of hot gas.
- Not far from M87 is a collection of galaxies arrayed in a pair of “chain-like” structures called “Markarian’s Chain”. These are visible to amateur observers with good-sized telescopes.
- The first ever image captured of a black hole was of the one at the heart of M87
The elliptical galaxy M87 is the home of several trillion stars, a supermassive black hole and a family of roughly 15,000 globular star clusters. For comparison, our Milky Way galaxy contains only a few hundred billion stars and about 150 globular clusters. The monstrous M87 is the dominant member of the neighboring Virgo cluster of galaxies, which contains some 2,000 galaxies. Discovered in 1781 by Charles Messier, this galaxy is located 54 million light-years away from Earth in the constellation Virgo. It has an apparent magnitude of 9.6 and can be observed using a small telescope most easily in May.
This Hubble image of M87 is a composite of individual observations in visible and infrared light. Its most striking features are the blue jet near the center and the myriad of star-like globular clusters scattered throughout the image.
The jet is a black-hole-powered stream of material that is being ejected from M87’s core. As gaseous material from the center of the galaxy accretes onto the black hole, the energy released produces a stream of subatomic particles that are accelerated to velocities near the speed of light.
At the center of the Virgo cluster, M87 may have accumulated some of its many globular clusters by gravitationally pulling them from nearby dwarf galaxies that seem to be devoid of such clusters today.