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In colliding galaxies, a pipsqueak shines bright



Bright green sources of high-energy X-ray light captured by NASA's NuSTAR mission are overlaid on an optical-light image of the Whirlpool galaxy (in the center of the image) and its companion galaxy, M51
b (the bright greenish-white spot above the whirlpool), taken by the Sloan Digital Sky Survey. Credit: NASA / JPL-Caltech, IPAC
    

In the nearby Whirlpool galaxy and its companion galaxy, M51b, two supermassive black holes heat up and devour surrounding material. These two monsters should be reviewed in NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) mission shows that a much smaller object is competing with the two behemoths.
                                

The galaxy-known M51a are two long, star-filled "arms" curling around the galactic center like ribbons. The much smaller M51b clings like a barnacle to the edge of the whirlpool. Collectively known as M51, the two galaxies are merging.

At the center of each galaxy is a supermassive black hole millions of times more massive than the Sun. The galactic merger should push huge amounts of gas and dust into those black holes and into orbit around them.

But neither black hole is radiating as brightly in the X.

-ray range as scientists would expect during a merger. Based on observations made by satellite that detect low-energy X-rays, NASA's Chandra X-ray Observatory, scientists have estimated that the layers of gas and dust are blocking extra emission. The new study, published in the Astrophysical Journal uses NuSTAR's high-energy X-ray vision to peer under these layers and found that the black hole is still dimmer than expected.

"I'm Still, Surprised by this finding, "said Murray Brightman, a researcher at Caltech, Pasadena, California. "Galactic mergers are likely to generate black hole growth, and the evidence of that would be high emission X-rays."

Brightman thinks that the most likely explanation is that black "flicker" during galactic mergers

"The flickering hypothesis is a new idea in the field," said Daniel Stern, a research scientist at NASA's Jet Propulsion Laboratory in Pasadena and the project scientist for NuSTAR. Figuring out how to short is an area of ​​active study. "

Small but Brilliant

Along with the two black holes radiating less than studied in M51a and M51b, the former also hosts an object that is millions of times smaller than either black hole yet is shining with equal intensity. X-ray landscape in M51.

The small X-ray source is a neutron star, an incredibly dense nugget of material left over after a massive star explodes at the end of its life. A typical neutron star is hundreds of times smaller than the sun-only as wide as a large city-yet has one to two times the mass. A teaspoon of neutron star material would weigh more than 1 billion tons.

Despite their size, they often make themselves known through intense light emissions. The neutron star found in M51 is even brighter than average and belongs to a newly discovered class of ultraluminous neutron stars. Brightman said he was responsible for the luminous emission; a previous paper by Brightman and colleagues about this neutron star supports that hypothesis. Some of the other bright, high-energy X-ray sources in these two galaxies could be neutron stars.
                                                                


Explore further:
                                        Cosmic collision forges galactic one ring in x-rays
                                    

More information:
                                        M. Brightman et al. A Long Hard-X-Ray Look at the Dual Active Galactic Nuclei of M51 with NuSTAR, The Astrophysical Journal (2018). DOI: 10.3847 / 1538-4357 / aae1ae
                                        

Journal reference:
                                                                                                            Astrophysical Journal
                                                        
                                                        
                                                                                                    

Provided by:
                                                                                                            Jet Propulsion Laboratory
                                                        

                                                        
                                                                                                    


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