Published: Sun, November 11, 2018
Sci-tech | By Patricia Wade

The first observation of the last stages of merging galaxies

The first observation of the last stages of merging galaxies

They can be produced, for instance, when black holes orbit each other or by the merging of galaxies.

For the first time, a team of astronomers has observed several pairs of galaxies in the final stages of merging together into single, larger galaxies.

Using powerful telescopes to see through the galaxies' thick walls of gas and dust surrounding their cores, the academics have managed - for the first time - to observe supermassive black holes fall into each other and coalesce into an even more giant black hole.

Our own Milky Way galaxy is now undergoing a merger with the neighboring Andromeda galaxy, and the supermassive black holes at the two galactic cores will eventually smash together, Koss said.

Next, the research team analyzed another catalog of galaxies from NASA's Hubble Space Telescope and the Keck Observatory in Hawaii whose X-ray signatures matched the Swift readings.

The images were taken by the Hubble Telescope's Wide Field Camera 3, and they show the galaxy NGC 6240. When galaxies collide, their monster black holes can unleash powerful energy in the form of gravitational waves, the kind of ripples in space-time that were just recently detected by ground-breaking experiments.

The images presage what will likely happen in our own cosmic backyard, in about a billion years, when our Milky Way merges with the neighboring Andromeda galaxy and their respective central black holes will smash together. Structure is giving way to chaos, but hiding behind this messy cloud of material are two supermassive black holes, nestled at the center of each of the galaxies, that are now excitingly close, giving astronomers the best view yet of the pair marching toward coalescence into one mega black hole. Astronomers searched ten years of data from the Burst Alert Telescope on the NASA Neil Gehrels Swift Observatory to search for visually obscured, active black holes. Using this tech, researchers were able to produce extremely sharp, near-infrared images of X-ray-producing black holes not found in the Hubble archive.

Keck was then called on to use its near-infrared vision to observe the x-ray producing black holes not found in the Hubble archive.

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The research team was first inspired by an image from the Hubble telescope that showed two galaxies almost combined into one, and it was used as the model for the study. The researchers were surprised to find such a high fraction of late-stage mergers, because most simulations suggest that black hole pairs spend very little time in this phase. They published the results in the journal Nature on November 8. Galaxy merger is a billion-plus-year process.

Laura Blecha, an assistant professor of physics at the University of Florida and a co-author of the study, commented:"The fact that black holes grow faster and faster as mergers progress tells us galaxy encounters are really important for our understanding of how these objects got to be so monstrously big".

It's not easy finding galaxy nuclei so close together either.

The research team looked for galaxies had active, luminous black holes obscured by large amounts of dust and gas. "With these observations, we can begin to explore the fraction of objects that are merging in the youngest, most distant regions of the universe - which should be fairly frequent".

Like a siren before a tsunami, gravitational waves reach Earth slightly earlier than light.

The team targeted galaxies with an average distance of 330 million light-years from Earth. The Webb telescope may also be able to look in mid-infrared light to uncover more galaxy interactions so encased in thick gas and dust that even near-infrared light can not penetrate them.

Something similar is expected to happen when our Milky Way galaxy crashes with the nearby Andromeda galaxy, though it's not expected to happen anytime soon, the researchers said. Right now, hardware is a huge limitation, but, once the James Webb Space Telescope is deployed in 2021, scientists will be able to measure masses, growth rates, and other physical parameters of black hole pairs.

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