In colliding galaxies, a pipsqueak shines bright

February 20, 2019, Jet Propulsion Laboratory
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, M51b (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 the most luminous X-ray sources in sight, but a new study using observations from NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) mission shows that a much smaller object is competing with the two behemoths.

The most stunning features of the Whirlpool galaxy—officially known as M51a—are the two long, star-filled "arms" curling around the 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 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. In turn, the intense gravity of the black holes should cause that orbiting material to heat up and radiate, forming 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. But the new study, published in the Astrophysical Journal, used NuSTAR's high-energy X-ray vision to peer below those layers and found that the black hole is still dimmer than expected.

"I'm still surprised by this finding," said study lead author Murray Brightman, a researcher at Caltech in Pasadena, California. "Galactic mergers are supposed to generate black hole growth, and the evidence of that would be strong emission of high-energy X-rays. But we're not seeing that here."

Brightman thinks the most likely explanation is that black holes "flicker" during galactic mergers rather than radiate with a more or less constant brightness throughout the process.

"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. "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."

Small but Brilliant

Along with the two radiating less than scientists anticipated 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. The two phenomena are not connected, but they do create a surprising 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 thousands of times smaller in diameter 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, 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 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 could also be .

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

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1.5 / 5 (8) Feb 20, 2019
How much material you can hide by forcing them into a small box! A limit soon comes when you look more and more ridiculous in doing so! The Big Bang box cannot hide any more stuff; no matter how much official cosmology ridicules itself!

It is the most clear case in which M51B is ejected with a clear trail and the two small X-ray sources are moving away from each other across a straight line from the site of ejection of M51B. This is the exact opposite of a "collision" scenario!

"Ambartsumian, Arp and the Breeding Galaxies":
2 / 5 (2) Feb 20, 2019
In search of black holes and dark matter astrophysicists are relying on indirect observations. It would seem that the measurement of the event horizon of a black hole directly would be a direct evidence. However, by the nature of a horizon, any real measurement of the event horizon will be indirect. The Event Horizon Telescope will get picture of the silhouette of the Sgr A* which is due to optical effects of spacetime outside of the event horizon. The result will be determined by the simple quality of the resulting image that does not depend on the properties of the spacetime within the image. So, it will be also indirect and an existence of BH is a hypothesis.
Da Schneib
3.7 / 5 (7) Feb 20, 2019
M51 is one of the more spectacular imaging targets in amateur astronomy.

This pulsed absorption by the SMBHs at the centers of M51a and M51b is a significant step forward in understanding galaxy mergers; the neutron star (probably a magnetar) is a side-issue. Astrophysics theorists will be dealing with this pulsation model for quite some time, I think. It's nice to see such a spectacular display yield some serious astrophysics.
1 / 5 (3) Feb 21, 2019
But the new study, ... to peer below those layers and found that the black hole is still dimmer than expected.

It is a grey hole, with minor light escaping radially. And for mergers, well you know...ridiculous.
But there was a surprise; the new data showed that the majority of these more common, less bright active galaxies, even looking back far into the past, were not triggered by mergers between galaxies.


"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.

See my comment under:
not rated yet Feb 21, 2019
okay tux. I think I can roughly understand your points.
If I am wrong? Do mot hesitate to correct me.

I am a Gravity wooist,
Nothing is getting out of a BH except gravitational attraction.

All the non-grav energy, including light & x-rays are being emitted from the vicinity of a BH. From the wreckage of the surrounding disk. Banging together to create sparks.

Second, Since the detectable (non-gravity wave) energies from the frictional forces of tetra-tonnage of individual rock & ruin constantly colliding in a random pandemonium?
I would guess that millions of years or longer for cooling off, would be a reasonable supposition after such a spasmodically stochastic conflagration.

I guess three, we can at least have a reasonable chance at doing something about an infalling rock. If our leadership were not debauched dunderheads.

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