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By looking through thick walls of gas and dust surrounding the messy nuclei of galaxies that merge, astronomers get their best vision, at the sight of tight pairs of supermassive black holes, as they walk towards coalescence in gigantic black holes.
A team of researchers led by Michael Koss of Eureka Scientific Inc., in Kirkland, Washington, conducted the largest investigation on the nuclei of nearby galaxies in a light near the end of the day. infrared, using high-resolution images taken by NASA's Hubble Space Telescope and WM Keck. Observatory in Hawaii. Hubble's observations represent more than 20 years of snapshots from his vast archive.
"Seeing the pairs of molten galaxy nuclei associated with these huge black holes so close to each other was rather amazing," Koss said. "In our study, we see two galaxy nuclei just at the moment the images were taken.You can not argue, it's a very" neat "result, which is not based on an interpretation."
The images also provide a close look at a phenomenon that was to be more common in the early universe when galaxy fusions were more common. When galaxies collide, their monster black holes can release powerful energy in the form of gravitational waves, the kind of wrinkles in space – time recently detected by unpublished experiments.
The new study also offers a glimpse of what will probably happen in our own cosmic backyard, in the billions of years, when our Milky Way will combine with the neighboring Andromeda galaxy and that their holes respective central blacks will break.
"Computer simulations of galaxy smashups show us that black holes grow faster during the final phases of mergers, at about the same time as black holes interact, and that's what we found in our investigation, "said Laura Blecha, a member of the study team, from the University of Florida, in Gainesville. "The fact that black holes are growing faster and faster as mergers progress tells us that galaxy encounters are really important to understand how these objects have become so gigantic."
A galaxy fusion is a slow process that lasts over a billion years. Two galaxies, under the intrepid attraction of gravity, dance one before the other to finally meet. The simulations reveal that galaxies emit a lot of gas and dust when they experience this wreckage in slow motion.
The ejected material often forms a thick curtain around the centers of coalescent galaxies, shielding them from visible light. Part of the material also falls on black holes in the heart of galaxies that merge. Black holes grow rapidly as they swallow their cosmic food and, in disordered eaters, they cause intense flare-up of the infalling gas. This rapid growth occurs in the 10 to 20 million years of the Union. The Hubble and Keck Observatory images captured close-up views of this final step, while the cluttered black holes are only separated by about 3,000 light-years – a near-embrace in terms cosmic.
It is not easy to find galaxy nuclei so close to each other. Most previous observations of colliding galaxies captured coalescing black holes in the early stages, whereas they were about 10 times farther apart. The late stage of the fusion process is so elusive, as the interacting galaxies are enclosed in dense dust and gas and require high-resolution observations in the infrared light that can see through the clouds and locate the locations of both molten nuclei.
The team first looked for visually darkened active black holes by sifting through a dozen years of X-ray data from the Burst Alert telescope (BAT) aboard the Neil Gehrels Swift telescope, NASA, a high-energy space observatory. "The gases that fall on the black holes emit X-rays and the brightness of these X-rays tells you how fast the black hole is developing," Koss said. "I did not know if we were going to find hidden fusions, but we suspected, based on computer simulations, that they would be in heavily enveloped galaxies, so we tried to look through the dust with them. clearest possible pictures, hoping to find mergers, black holes. "
The researchers searched the Hubble Archives, identifying the merging galaxies identified in the X-ray data. They then used the ultra-thin, near-infrared vision of the Keck Observatory to observe a larger sample of black x-ray producing holes not found in the Hubble Archives.
"People had already done studies to look for these closely interacting black holes, but what really made this study possible is the X-rays that can pierce the cocoon of dust," Koss said. "We also looked a little further into the universe to be able to explore a larger volume of space, giving us a greater chance of finding brighter, faster-growing black holes."
The team targeted galaxies at an average distance of 330 million light-years from Earth. Many galaxies have sizes similar to those of the Milky Way and Andromeda. The team analyzed 96 galaxies from the Keck Observatory and 385 Hubble archive galaxies found in 38 different Hubble observation programs. The galaxy samples are representative of what astronomers would find by conducting an open survey.
To check their results, the Koss team compared study galaxies to 176 other Hubble archives galaxies, devoid of growing black holes. The comparison confirmed that the luminous nuclei found in the dusting galaxies interacting researchers are the signature of pairs of rapidly growing black holes leading to a collision.
When the two supermassive black holes of each of these systems come together in millions of years, their encounter will produce strong gravitational waves. The gravitational waves produced by the collision of two black stellar mass holes have already been detected by the gravitational laser interference observatory (LIGO). Observatories such as NASA / ESA's NASA / ESA Spatial Antenna Spacecraft (LISA) will be able to detect low-frequency gravitational waves generated by supermassive black hole fusions, which are a million times more than those detected by LIGO.
Future infrared telescopes, such as NASA's James Webb Space Telescope and a new generation of ground-based giant telescopes, will provide an even better probe of collisions in dusty galaxies by measuring masses, growth rate and pair dynamics black holes close. The Webb telescope may also be able to look in the middle infrared light to discover more galaxy interactions so much enclosed in a thick gas and dust that even near infrared light can not penetrate them.
The results of the team will be published online in the November 7, 2018 issue of Nature.
The Hubble Space Telescope is an international cooperation project between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, operates the telescope. The Institute of Space Telescope Sciences (STScI) in Baltimore, Maryland, conducts Hubble's scientific activities. The STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.
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