In colliding galaxies, a Pipsqueak shines brightly

Whirlpool galaxy and its galaxy companion, M51b, two supermassive black holes
warm and devour the surrounding material. These two monsters should be the most
bright X-ray sources in sight, but a new study using NASA's NuSTAR observations
Mission (network of nuclear spectroscopic telescopes) shows that a much smaller object
is in competition with the two behemoths.

amazing features of the Whirlpool galaxy – officially known as the M51a – are the
two "arms" filled with stars around the galactic center as
ribbons. The M51b, much smaller, clings like a goose to the edge of the
Tourbillon. Collectively known as M51, the two galaxies merge.

In the center
of each galaxy is a supermassive black hole millions of times more massive than
the sun. Galactic fusion is expected to introduce huge amounts of gas and dust into the
black holes and orbiting them. In turn, the intense gravity of the
Black holes should cause the heating and radiation of this material in orbit.
bright discs around everyone that can eclipse all the stars in their galaxies.

But neither
black hole radiates as brightly in the x-ray range that scientists expect
during a merger. Based on previous observations of satellites that detect
Low energy x-rays, such as those from NASA Chandra X-ray
, scientists believed that layers of gas and dust around
the black hole in the largest galaxy blocked an additional broadcast. But the new
This study, published in the Astrophysical Journal, used NuSTAR's high-energy X-rays.
vision to look below these layers and found that the black hole is always lower
provided that.

"I am
always surprised by this discovery, "said lead author Murray Brightman,
researcher at Caltech in Pasadena California. "Galactic mergers are
supposed to generate black hole growth, and proof of that would be strong
high energy X-ray emission. But we do not see that here. "

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

flickering hypothesis is a new idea on the ground, "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 variability of black holes
it's been produced on time scales of millions of years, but now we think about these time scales
could be much shorter. Determining how short it is is an active field of study. "

Small but brilliant

In the same way
the two black holes emitting less than the scientists anticipated in M51a and M51b,
the first one also hosts an object that is millions of times smaller than
black hole shines yet with the same intensity. Both phenomena are not
connected, but they create a surprising X-ray landscape in M51.

The little
The X-ray source is a neutron star, an incredibly dense nugget of materials left behind
ends after a massive star explodes at the end of his life. A typical neutron
the star is hundreds of thousands of times smaller in diameter than the sun – only
as wide as a big city – but has one to two times the mass. A teaspoon of
the material of neutron stars would weigh more than a billion tons.

Despite their
size, neutron stars are often noticed by intense light
shows. The neutron star found in M51 is even brighter than the average and belongs to
to a newly discovered class known as ultraluminous neutron stars. Brightman
some scientists have proposed that the powerful magnetic fields generated by the
the neutron star could be responsible for the light emission; a previous article
by Brightman and his colleagues about this neutron star supports this hypothesis. Some
other bright and high-energy X-ray sources observed in these two galaxies could
also be neutron stars.

NuSTAR is a
Small exploratory mission led by Caltech and managed by JPL for NASA science
Mission Direction in Washington. NuSTAR was developed in partnership with the
Danish Technical University and the Italian Space Agency (ASI). The spaceship
was built by Orbital Sciences Corporation in Dulles, Virginia (now part of
Northrop Grumman). The NuSTAR Mission Operations Center is located at UC Berkeley, and
the official data archives are in the scientific archives of NASA's high energy astrophysics
Research Center. ASI provides the ground station of the mission and a mirror
archive. Caltech manages JPL for NASA

For more information on NuSTAR, visit:

Media contact

Calla Cofield
Jet Propulsion Laboratory, Pasadena, California
[email protected]


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