From NASA NuSTAR: “NASA’s NuSTAR Captures Possible ‘Screams’ from Zombie Stars”

NASA NuSTAR
NuSTAR

April 29, 2015
Felicia Chou
Headquarters, Washington
202-358-0257
felicia.chou@nasa.gov

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov

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NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, has captured a new high-energy X-ray view (magenta) of the bustling center of our Milky Way galaxy. The smaller circle shows the area where the NuSTAR image was taken — the very center of our galaxy, where a giant black hole resides. That region is enlarged to the right, in the larger circle, to show the NuSTAR data.
The NuSTAR picture is one of the most detailed ever taken of the center of our galaxy in high-energy X-rays. The X-ray light, normally invisible to our eyes, has been assigned the color magenta. The brightest point of light near the center of the X-ray picture is coming from a spinning dead star, known as a pulsar, which is near the giant black hole. While the pulsar’s X-ray emissions were known before, scientists were surprised to find more high-energy X-rays than predicted in the surrounding regions, seen here as the elliptical haze. Astronomers aren’t sure what the sources of the extra X-rays are, but one possibility is a population of dead stars. The background picture was captured in infrared light by NASA’s Spitzer Space Telescope.
The NuSTAR image has an X-ray energy range of 20 to 40 kiloelectron volts.
Image credit: NASA/JPL-Caltech

Peering into the heart of the Milky Way galaxy, NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) has spotted a mysterious glow of high-energy X-rays that, according to scientists, could be the “howls” of dead stars as they feed on stellar companions.

“We can see a completely new component of the center of our galaxy with NuSTAR’s images,” said Kerstin Perez of Columbia University in New York, lead author of a new report on the findings in the journal Nature. “We can’t definitively explain the X-ray signal yet — it’s a mystery. More work needs to be done.”

The center of our Milky Way galaxy is bustling with young and old stars, smaller black holes and other varieties of stellar corpses – all swarming around a supermassive black hole called Sagittarius A*.

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Sagittarius A*. This image was taken with NASA’s Chandra X-Ray Observatory. Ellipses indicate light echoes.

NASA Chandra Telescope
Chandra

NuSTAR, launched into space in 2012, is the first telescope capable of capturing crisp images of this frenzied region in high-energy X-rays. The new images show a region around the supermassive black hole about 40 light-years across. Astronomers were surprised by the pictures, which reveal an unexpected haze of high-energy X-rays dominating the usual stellar activity.

“Almost anything that can emit X-rays is in the galactic center,” said Perez. “The area is crowded with low-energy X-ray sources, but their emission is very faint when you examine it at the energies that NuSTAR observes, so the new signal stands out.”

Astronomers have four potential theories to explain the baffling X-ray glow, three of which involve different classes of stellar corpses. When stars die, they don’t always go quietly into the night. Unlike stars like our sun, collapsed dead stars that belong to stellar pairs, or binaries, can siphon matter from their companions. This zombie-like “feeding” process differs depending on the nature of the normal star, but the result may be an eruption of X-rays.

According to one theory, a type of stellar zombie called a pulsar could be at work. Pulsars are the collapsed remains of stars that exploded in supernova blasts. They can spin extremely fast and send out intense beams of radiation. As the pulsars spin, the beams sweep across the sky, sometimes intercepting the Earth, like lighthouse beacons.

“We may be witnessing the beacons of a hitherto hidden population of pulsars in the galactic center,” said co-author Fiona Harrison of the California Institute of Technology (Caltech) in Pasadena, and principal investigator of NuSTAR. “This would mean there is something special about the environment in the very center of our galaxy.”

Other possible culprits include heavy-set stellar corpses called white dwarfs, which are the collapsed, burned-out remains of stars not massive enough to explode in supernovae. Our sun is such a star, and is destined to become a white dwarf in about five billion years. Because these white dwarfs are much denser than they were in their youth, they have stronger gravity and can produce higher-energy X-rays than normal. Another theory points to small black holes that slowly feed off their companion stars, radiating X-rays as material plummets down into their bottomless pits.

Alternatively, the source of the high-energy X-rays might not be stellar corpses at all, astronomers say, but rather a diffuse haze of charged particles, called cosmic rays. The cosmic rays might originate from the supermassive black hole at the center of the galaxy as it devours material. When the cosmic rays interact with surrounding, dense gas, they emit X-rays.

However, none of these theories match what is known from previous research, leaving the astronomers largely stumped.

“This new result just reminds us that the galactic center is a bizarre place,” said co-author Chuck Hailey of Columbia University. “In the same way people behave differently walking on the street instead of jammed on a crowded rush hour subway, stellar objects exhibit weird behavior when crammed in close quarters near the supermassive black hole.”

The team says more observations are planned. Until then, theorists will be busy exploring the above scenarios or coming up with new models to explain what could be giving off the puzzling high-energy X-ray glow.

“Every time that we build small telescopes like NuSTAR, which improve our view of the cosmos in a particular wavelength band, we can expect surprises like this,” said Paul Hertz, the astrophysics division director at NASA Headquarters in Washington.

NuSTAR is a Small Explorer mission led by Caltech and managed by NASA’s Jet Propulsion Laboratory in Pasadena, California, for NASA’s Science Mission Directorate in Washington.

More information is online at:

http://www.nasa.gov/nustar

See the full article here.

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NuSTAR is a Small Explorer mission led by the California Institute of Technology in Pasadena and managed by NASA’s Jet Propulsion Laboratory, also in Pasadena, for NASA’s Science Mission Directorate in Washington. The spacecraft was built by Orbital Sciences Corporation, Dulles, Va. Its instrument was built by a consortium including Caltech; JPL; the University of California, Berkeley ; Columbia University, New York; NASA’s Goddard Space Flight Center, Greenbelt, Md.; the Danish Technical University in Denmark; Lawrence Livermore National Laboratory, Livermore, Calif.; ATK Aerospace Systems, Goleta, Calif., and with support from the Italian Space Agency (ASI) Science Data Center.

NuSTAR’s mission operations center is at UC Berkeley, with the ASI providing its equatorial ground station located at Malindi, Kenya. The mission’s outreach program is based at Sonoma State University, Rohnert Park, Calif. NASA’s Explorer Program is managed by Goddard. JPL is managed by Caltech for NASA.

Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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