In colliding galaxies, a pipsqueak shines bright

A much smaller object is competing with the two behemoths.


In the nearby Whirlpool galaxy and its companion universe, M51b, two supermassive black holes heat up and devour encompassing material. These two beasts ought to be the most luminous X-ray sources in sight, however, another investigation utilizing perceptions from NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) mission demonstrates that a lot littler article is contending with the two behemoths.

Every center of the galaxy contains a supermassive black hole- millions time massive than Sun. The galactic merger must push huge amounts of gas and dust into those black holes and into orbit around them. As a result, intense gravity may cause orbiting material to heat up and radiate to create bright disks around each that can outshine all the stars in their galaxies.

But neither black hole is radiating as brightly in the X-ray range as scientists would expect during a merger. Based on earlier observations from satellites that detect low-energy X-rays, such as NASA’s Chandra X-ray Observatory, scientists believed that layers of gas and dust around the black hole in the larger galaxy were blocking extra emission.

In a new study, scientists used observations from NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) mission and show that below those layers and found that the black hole is still dimmer than expected.

Daniel Stern, a research scientist at NASA‘s Jet Propulsion Laboratory in Pasadena said, “The flickering hypothesis is a new idea in the field. We used to think that the black hole variability occurred on timescales of millions of years, but now we’re thinking those timescales could be much shorter. Figuring out how short is an area of active study.”

In addition to these two black holes, the former also consists of an object that is millions of times smaller than either black hole yet is shining with equal intensity. However, both phenomena are not connected but generate a surprising X-ray landscape in M51.

The little X-ray source is a neutron star, an extraordinarily dense nugget of material left over after a massive star detonates at the end of its life. A common neutron star is a huge number of times littler than the Sun, yet has one to multiple times the mass. A teaspoon of neutron star material would gauge more than 1 billion tons.

Despite their size, neutron stars 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 known as ultraluminous neutron stars.

Brightman said, “Some scientists have proposed that strong magnetic fields generated by the neutron star could be 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 seen in these two galaxies could also be neutron stars.”

NuSTAR is a Small Explorer mission led by Caltech and managed by JPL for NASA’s Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corporation in Dulles, Virginia (now part of Northrop Grumman). NuSTAR’s mission operations center is at UC Berkeley, and the official data archive is at NASA’s High Energy Astrophysics Science Archive Research Center. ASI provides the mission’s ground station and a mirror archive.

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