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For the first time, astronomers observed the final stages of galactic fusions, peering through thick walls of gas and dust to see pairs of supermassive black holes getting closer and the rapid growth of these black holes.
In the center of most, if not all, galaxies are supermassive black holes whose masses are millions, even billions of times greater than those of the Earth's sun. For example, at the heart of our galaxy of the Milky Way is Sagittarius A *, with a mass of about 4.5 million solar masses.
Previous work has shown that galaxy fusion can help fuel the growth of supermassive black holes. This research suggests that black holes at the heart of colliding galaxies can combine to become even larger black holes. [When Galaxies Collide: Photos of Great Galactic Crashes]
Galactic fusions probably offer supermassive black holes many opportunities to tear stars and devour the material. Such destruction releases extraordinary amounts of light and probably serves as a motor for the quasars, which are among the brightest objects in the universe.
However, the authors of the new work expressed mixed support for the supermassive black hole growth model, based on fusion. While some research has shown a link between quasars and fused galaxies, other studies have found no such association.
One possible explanation for the apparent lack of a link between quasars and fusing galaxies is that the gas and dust swirling around these galaxies can strongly obscure black holes. This would be true even at the beginning of the mergers, when the galaxies are separated by more than 16 000 light-years from space. Computer simulations suggest that this concealment peaks during the later stages of fusion, when the galactic nuclei are separated by less than 10,000 light-years, said the study's authors.
Now, researchers have observed several pairs of galaxies at the end of fusion, their supermassive black holes getting closer. The results show how even bigger black holes could occur.
Scientists first searched for hidden black holes by sifting X-ray data collected for ten years at NASA's Neil Gehrels Swift observatory. When black holes devour material, such "active" black holes can generate visible high-energy X-rays even through thick clouds of gas and dust.
Next, the researchers searched for galaxies corresponding to these X-ray discoveries by analyzing data from NASA's Hubble Space Telescope and the Keck Observatory in Hawaii. Computer-controlled deformable mirrors, a technology called adaptive optics from the Keck Observatory help to sharpen the images of the stars, "resulting in a considerable increase in resolution," Space.com told the author principal of the study, Michael Koss. Koss is an astrophysicist with the Eureka Scientific Scientific Research Society in Oakland, California.
"It would be like moving from Vision 20/200 where you are legally blind to 20/20 vision, helping us to see the galaxies with incredible detail," he said.
The disordered nuclei of these colliding galaxies hide the final stage of the fusion of two galactic nuclei. Above: NGC 6240, reproduced by Hubble's Wide Field Camera 3, associated with a close-up of the galactic cores in infrared light by the Keck Observatory in Hawaii. The images of the other four galaxies are made by the pan-tilt telescope and the pan-STARRS and Keck.
Credit: Mr. Koss (Eureka Scientific, Inc.) / NASA / ESA; Keck images: Mr. Koss (Eureka Scientific, Inc.) / W.M. Keck Observatory; Pan-STARRS Images: M. Koss (Eureka Scientific, Inc.) / Panoramic Survey Telescope and Rapid Response System
In total, scientists analyzed 96 galaxies observed with the Keck Observatory and 385 galaxies from the Hubble Archive. All these galaxies are located on average 330 million light-years away from the Earth, relatively close to one another cosmically, and many of them are similar in size to the Milky Way. .
The researchers found that more than 17% of these galaxies harbored a pair of black holes in their center, signs of the later stages of a galactic fusion. These results corresponded to the computer simulations of the researchers, who suggested that highly active but highly hidden black holes hidden in galaxies rich in gas and dust were responsible for many mergers of supermassive black holes.
"Galactic fusions could be a vital way to grow black holes," said Koss.
Our own galaxy, the Milky Way, is fusing with the neighboring Andromeda galaxy, and the supermassive black holes of the two galactic nuclei will eventually crash, Koss said.
"At this moment, the galaxies are separated by millions of light-years, but we are moving towards Andromeda at 250 000 km / h [400,000 km/h]"In 6 billion years, there will be no galaxy of the Milky Way or Andromeda – just a big galaxy."
The much awaited NASA James Webb Space Telescope, due to be launched in 2021, offers an even better view of mergers in dusty and darkened galaxies. The enhanced images could also come from adaptive optics systems of the next generation of very large ground-based telescopes, such as the 30-meter telescope, the very large European telescope and the giant Magellan telescope, Koss said. The James Webb Space Telescope should also be able to measure the masses, growth rates and other physical characteristics of each member of pairs of nearby black holes, according to the researchers.
The new work was detailed online today (November 7) in the journal Nature.
Follow Charles Q. Choi on Twitter @cqchoi. Follow us on twitter @Spacedotcom and on Facebook. Original article on Space.com.
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