Avi Blizovsky
Two images taken by Hubble of the 20 nearby quasars - one has a host galaxy and the one on the left - the homeless black hole.
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The Hubble Space Telescope discovered in collaboration with the European Space Agency's VLT Large Telescope in Chile, a supermassive black hole without a galaxy surrounding it. These black holes are usually associated with galaxies, so this is an unusual discovery.
One possibility is that the galaxy was torn from it in a collision with another galaxy. Another possibility is that the black hole is indeed surrounded by matter, but it is a form of dark matter that Hubble cannot detect.
The discovery was made during a joint survey by Hubble and the VLT - the very large telescope in Chile operated by the European Space Agency.
This is the first convincing evidence for the existence of such an object - a bright quasar. And now hypotheses are put forth from various hypotheses and as mentioned the strangest of them is that the galaxy exists but is composed of dark matter that Hubble is unable to detect.
Quasars are huge and relatively distant sources that emit a tremendous amount of radiation. They are mainly associated with galaxies that contain a massive central black hole.
The team surveyed 20 relatively close quasars in detail. In 19 of them, they found, as expected, that these massive black holes are surrounded by their host galaxy. However, the bright quasar HE0450-2958, which is half a billion light-years away from us, is not surrounded by any galaxy.
Supermassive black holes are bodies that are hundreds of millions of times more massive than the Sun. They are often found in the centers of the most massive galaxies, including our Milky Way. These black holes grow even larger by devouring matter from their surroundings.
The objects of this type, the winners of the best feeding are called quasars - star-like objects - because initially they shine like stars.
In the observations made in the last century, and in particular those made in Hubble, showed that quasars are usually associated with galaxies that have a large black hole. However, viewing the quasar's host galaxy is a challenging task because the quasar blinds the light coming from the host galaxy.
To overcome the problem, the astronomers used a new efficient strategy. A combination of ultra-sharp images of Abel as well as spectroscopy from the VLT telescope. They combined images of 20 quasars at the same time they also imaged a reference star. It is designed to help filter the light of the quasar and separate it from the light of the galaxy.
Despite the use of all new techniques, no host galaxy was discovered around HE0450-2958. This means that if such a galaxy exists it should be 6 times fainter than typical host galaxies. Or its radius is less than 300 light years (a typical galaxy like this can be 6,000 to 50 light years in diameter).
"With the powerful combination of Hubble and the VLT we can be sure that we would have discovered a normal galaxy if it existed," said Pierre Magain of the University of Liège in Belgium.
The European Space Agency's announcement on the Universe Today website
They knew the black holes
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