For the first time, astronomers have noticed the final stages of galactic mergers, looking through dense gas and dust walls, to see pairs of oversized black holes approaching and the rapid growth of black holes.
The centers of most, if not all, galaxies are oversized black holes with masses that are millions to billions of times those of the Earth's sun. For example, in the heart of our galaxy is the Sagittarius A *, which is about 4.5 million solar masses.
Previous work has shown that fusion of galaxies could help increase oversized black holes. This research suggested that black holes in the nuclei of colliding galaxies can be combined to make even larger black holes. [When Galaxies Collide: Photos of Great Galactic Crashes]
Galactic mergers are likely to produce oversized black holes with ample opportunities to break the stars and devour the matter. Such destruction releases exceptional amounts of light and probably serves as the driving force behind quasars, which are ranked among the brightest objects in the universe.
However, support for the model based on merging the development of oversized black holes has been shown mixed, the authors of the new work reported. While some research has shown a relationship between quasar and merging galaxies, other studies have not found such a link.
One possible explanation for the apparent lack of connection between quasars and fused galaxies is that the gas and dust swirling around these galaxies are likely to cover the black holes. This would be true even in the early stages of mergers when galaxies are separated by more than 16,000 light-years. Computer simulations suggest that such hiding peaks during the final stages of fusions, when the galactic nuclei are less than 10,000 light-years away, the authors of the study reported.
Now, researchers have seen several galaxy pairs in the late stages of the merger, while their cores are over-sized black holes coming closer. The findings shed light on how even more massive black holes could arise.
Scientists searched for hidden black holes for the first time, X-ray X-ray data sifting from NASA's Neil Gehrels Swift Observatory. When black holes devour matter, such "active" black holes can generate high-energy X-rays that are visible even through dense clouds of gas and dust.
Then, the researchers looked at the galaxies that match these X-ray findings, combining NASA's Hubble Space Telescope and Keck Observatory data in Hawaii. Computer-disfigured mirrors, a technology called adaptive view at the Keck Observatory, help sharpen the images of stars, "leading to a huge increase in resolution," said Michael Koss at Space.com. Koss is an astrophysicist at the Eureka Scientific research firm in Auckland, California.
"It would be like going from the 20/200 vision where you are legally blind to a 20/20 vision, helping us see galaxies in incredible detail," he said.
Altogether, scientists analyzed 96 galaxies observed with the Keck Observatory and 385 galaxies from Hubble. All these galaxies are on average 330 million light-years from Earth, relatively close to the cosmic level, with many similar in size to the Milky Way.
The researchers found that over 17% of these galaxies hosted a pair of black holes in their centers, signs of the late stages of a galactic merger. These findings match the computational simulations of the researchers, which suggest that the very active but heavy black holes hidden in the gas-rich galaxies are responsible for many mergers of oversized black holes.
"Galaxy mergers can be a major way of developing black holes," said Koss.
Our galaxy galaxy is in a merger with the neighboring Andromeda galaxy and the oversized black holes in the two galaxy nuclei will eventually break together, said Koss.
"At the moment, galaxies are separated by millions of light years, but we are moving towards Andromeda at 250,000 mph [400,000 km/h], Said Koss. "In 6 billion years, there will be no galaxy Galaxy and Andromeda Galaxy – a great galaxy."
An even better picture of mergers in dusty, heavily fuzzy galaxies can come from NASA's highly anticipated James Webb space telescope designed for launch in 2021. Enhanced images could also come from adaptive optics systems in the next generation of very large terrestrial telescopes , such as the Thirty-Telescope Telescope, the European Extremely Large Telescope and the Giant Magellan Telescope, said Koss. James Webb Space Telescope should also be able to measure masses, growth rates and other physical characteristics for each member of the black hole pair, according to the researchers.
The new project was analyzed online today (November 7th) in Nature magazine.