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Posted on 14 Apr 2019
"When I saw the image of this galaxy for the first time in Hubble, I immediately knew that it was unusual," said Marc Postman, of the company. Institute of Space Telescope Science, about the monster elliptical galaxy, with a central core larger than anything that had been seen before. "The nucleus was very diffuse and very big. The challenge then was to make sense of all the data, given what we knew from Hubble's previous observations, and to find a plausible explanation of the intriguing nature of this particular galaxy. "
Seven years before this image of the gargantuan black hole at the heart of the M87 galaxy by Event Horizon Telescope, astronomers using the NASA / ESA Hubble Space Telescope in the fall of 2012 had achieved a remarkable view of a galaxy elliptical monster, located in a few years, the galaxy is the most massive and brilliant galaxy of the Abell 2261 group, with a nucleus bigger than ever. Expanding on a little over a million light-years away, the galaxy has about ten times the diameter of the galaxy's Milky Way. The blistered galaxy is part of an unusual class of galaxies filled with a stellar fog of light where a peak of concentrated light would normally occur around a central black hole.
The size of a galaxy's nucleus is usually correlated to the dimensions of the host galaxy, but in this case the central region is much larger than astronomers could expect for galaxy size. In fact, the inflated nucleus is more than three times larger than the center of other very bright galaxies.
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"Expecting to find a black hole in every galaxy, it's a bit like waiting to find a hole in a peach," says astronomer Tod Lauer of the National Observatory of Tucson Optical Astronomy. "With this Hubble sighting, we cut into the biggest catch and we can not find the pit. We do not know for sure that the black hole is not there, but Hubble shows that there is no concentration of stars in the nucleus. "
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Seeing the nucleus, it's like seeing a city without a center, just houses scattered over a vast landscape. An international team of astronomers has used the Hubble Investigation Advanced Camera and the Hubble Wide Field Camera 3 to measure the amount of starlight across the galaxy, cataloged 2MASX J17222717 + 3207571 but more commonly referred to as A2261- BCG. .
Hubble's observations revealed that the inflated galaxy core, measuring about 10,000 light-years, is the largest ever seen. Astronomers using NASA's Hubble Space Telescope have obtained a remarkable new view of this giant of an elliptical galaxy that could have been inflated by the actions of one or more black holes in its nucleus. Covering a little more than a million light-years away, the galaxy has about 10 times the diameter of our Milky Way galaxy.
Seeing the core, it's like seeing a city without a city center, just houses scattered over a vast landscape.
Astronomers have proposed two possibilities for the inflated nucleus. One scenario is that a pair of merging black holes has gravitationally stirred and scattered the stars. Another idea is that the merging black holes have been ejected from the nucleus. Left without an anchor, the stars began to spread even more, creating the puffy nucleus.
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Previous observations by Hubble have revealed that supermassive black holes, with masses millions or billions of times greater than those of the Sun, reside in the center of almost all galaxies and can play a role in the formation of these central regions.
Astronomers expected to see a slight rush of light in the center of the galaxy, marking the location of the black hole and corresponding stars. Instead, the intensity of starlight has remained fairly uniform throughout the galaxy. One possibility for the inflated core may be due to two central black holes in orbit.
These black holes collectively could have been as massive as several billion suns. One of the black holes would be native to the galaxy, while the second could have been added from a smaller galaxy engulfed by the gigantic elliptical.
In this scenario, the stars surrounding the center of the giant galaxy are approaching the two black holes. The stars then received a gravitational start of the nucleus. Each gravitational slingshot deprives the black holes of momentum, bringing the two players closer together until they merge to form a single supermassive black hole that still resides in the center of the galaxy.
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Another related possibility is that the fusion of black holes has created gravity waves, which are ripples in the structure of the space. According to the theory of general relativity, a pair of black holes that merge produces ripples of gravity that disappear. If the black holes have unequal mass, a portion of the energy can then radiate more strongly in one direction, providing the equivalent of a rocket thrust. The imbalance of forces would have ejected the fused black hole from the center at speeds of millions of kilometers at the time, which would have made the galaxy without a central black hole.
"The black hole is the anchor point of the stars," says Laurer, co-author of Hubble's study and member of the Nuker team: Hubble Space Telescope surveys on centers of galaxies. "If you remove it, you suddenly have a lot less mass. The stars do not stand together very well and they move outward, further widening the core. "
The team admits that the ejected black hole scenario may sound far-fetched, "but that's what makes the observation of the Universe so intriguing: sometimes, one finds the unexpected," Postman says. .
"It's a good enough system to ask a lot of questions," added Lauer.
"We thought a lot about what black holes do. But we could not test our theories. This is an interesting place where many of our ideas can be gathered and tested, along with some pretty exotic ideas about how black holes can interact dynamically and how they will affect the surrounding stellar population. .
The Abell 2261 cluster is part of a multi-wavelength survey, led by Postman, called Cluster Lensing And Supernova Investigation with Hubble (CLASH). The survey examines the distribution of dark matter in 25 clusters of massive galaxies.
The huge cluster of galaxies Abell 2744, nicknamed Pandora's Cluster, takes on a ghostly look in this NASA / ESA Hubble Space Telescope view at the top of the page. In this image, the total light of the group's stars has been artificially colored in blue. This reveals that all starlight is not contained in the cities of stars – galaxies – that appear as bright blue-white spots. A fraction of the starlight is also scattered in the group, as in the darker blue regions.
This light comes from dead galaxies. The galaxies were torn a long time ago by the group's gravitational forces and their stars scattered in what is called the Intracluster space – the space between the galaxies.
These orphan stars roam the group, without being gravitationally attached to a single galaxy. Since these extremely pale stars are the brightest at near-infrared wavelengths, this type of observation is only possible with Hubble's infrared sensitivity at extremely low light. Galaxies that are not stained blue are either in the foreground or in the background and are not part of the cluster.
The Daily Galaxy via provided by NASA / Hubble Space Science Institute
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