Mysterious Ultra Luminous X-Ray Sources Keep Space Scientists Guessing

Space scientists have debated the nature and origin of high energy ultra-luminous x-ray sources for years  

This image from Swift's X-Ray Telescope captures both of the known ULXs in M31. The first, dubbed CXOM31 J004253.1+411422, was discovered with NASA's Chandra X-ray Observatory on Dec. 17, 2009, and appears to be a stellar-mass black hole. The other, named XMMU J004243.6+412519, was discovered just last month, on Jan. 15, by the European Space Agency's XMM-Newton spacecraft. Credit: NASA/Swift/Stefan Immler
This image from Swift’s X-Ray Space Telescope captures both of the known ULXs in M31. The first, dubbed CXOM31 J004253.1+411422, was discovered with NASA’s Chandra X-ray Space Observatory on Dec. 17, 2009, and appears to be a stellar-mass black hole. The other, named XMMU J004243.6+412519, was discovered just last month, on Jan. 15, by the European Space Agency’s XMM-Newton spacecraft. Credit: NASA/Swift/Stefan Immler

Space news (Oct. 28, 2014) –

Space scientists have been looking at celestial objects called ultraluminous x-ray sources (ULXs) for years in search of answers to the mystery surrounding their nature and origin. Celestial bodies radiating enormous amounts of high-energy x-rays, astronomers have been studying three nearby ULXs changing thoughts and present theory on these energetic characters.  

Space scientists using the Chandra X-ray Observatory, Hubble Space Telescope, Swift Gamma-ray Burst Explorer and XMM-Newton Space Observatory have been studying two ULXs discovered in Andromeda galaxy (M31). The first is called CXOM31 and was discovered in 2009 using the Chandra X-ray Space Observatory. The second, XMMU, was discovered on Jan. 15, 2014 by the European Space Agency’s XMM-Newton spacecraft.   

The locations of two M31 ULXs are shown on this optical image of our galactic neighbor. M31 lies 2.5 million light-years away in the constellation Andromeda and is the nearest large spiral galaxy to our own. Under a clear, dark sky, it can be seen as a misty patch with the naked eye. Credit: NASA/Swift; background: Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF
The locations of two M31 ULXs are shown on this optical image of our galactic neighbor. M31 lies 2.5 million light-years away in the constellation Andromeda and is the nearest large spiral galaxy to our own. Under a clear, dark sky, it can be seen as a misty patch with the naked eye. Credit: NASA/Swift; background: Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF

Space scientists believe both ULXs they observe in Andromeda are binary star systems with a black hole rapidly accreting (consuming) material from its neighbor at a rate near the theoretical Eddington limit (the maximum accretion rate of a black hole).  

“There are four black hole binaries within our own galaxy that have been observed accreting at these extreme rates,” said Matthew Middleton, an astronomer at the Anton Pannekoek Astronomical Institute in Amsterdam. “Gas and dust in our own galaxy interfere with our ability to probe how matter flows into ULXs, so our best glimpse of these processes comes from sources located out of the plane of our galaxy, such as those in M31.”  

“As gas spirals toward a black hole, it becomes compressed and heated, eventually reaching temperatures where it emits X-rays. As the rate of matter ingested by the black hole increases, so does the X-ray brightness of the gas. At some point, the X-ray emission becomes so intense that it pushes back on the inflowing gas, theoretically capping any further increase in the black hole’s accretion rate. Astronomers refer to this as the Eddington limit, after Sir Arthur Eddington, the British astrophysicist who first recognized a similar cutoff to the maximum luminosity of a star.”  

“Black-hole binaries in our galaxy that show accretion at the Eddington limit also exhibit powerful radio-emitting jets that move near the speed of light,” Middleton said. “Although astronomers know little about the physical nature of these jets, detecting them at all would confirm that the ULX is accreting at the limit and identify it as a stellar mass black hole.”  

High-energy X-rays streaming from a rare and mighty pulsar (magenta), the brightest found to date, can be seen in this new image combining multi-wavelength data from three telescopes. The bulk of a galaxy called Messier 82 (M82), or the
High-energy X-rays streaming from a rare and mighty pulsar (magenta), the brightest found to date, can be seen in this new image combining multi-wavelength data from three telescopes. The bulk of a galaxy called Messier 82 (M82), or the “Cigar galaxy,” is seen in visible-light data captured by the National Optical Astronomy Observatory’s 2.1-meter telescope at Kitt Peak in Arizona. Starlight is white, and lanes of dust appear brown. Low-energy X-ray data from NASA’s Chandra X-ray Space Observatory are colored blue, and higher-energy X-ray data from NuSTAR are pink.

Space scientists operating NASA’s Nuclear Array (NuSTAR) have also found the brightest ULX on record near the center of galaxy Messier 82 (M82) 12 million light-years away. Called M82 X-2, they believe this particular object is actually a dead pulsating star called a pulsar, rather than a binary star system with a black hole accreting material from its neighbor.  

“Astronomers have found a pulsating, dead star beaming with the energy of about 10 million suns. This is the brightest pulsar – a dense stellar remnant left over from a supernova explosion – ever recorded. The discovery was made with NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR.”  

“You might think of this pulsar as the ‘Mighty Mouse’ of stellar remnants,” said Fiona Harrison, the NuSTAR principal investigator at the California Institute of Technology in Pasadena, California. “It has all the power of a black hole, but with much less mass.”  

This ULX being something other than a binary star system with an accreting black hole is surprising to astronomers. They’ll have to rethink present theories on the nature and origin of these mysterious celestial objects.   

“The pulsar appears to be eating the equivalent of a black hole diet,” said Harrison. “This result will help us understand how black holes gorge and grow so quickly, which is an important event in the formation of galaxies and structures in the universe.”  

“ULXs are generally thought to be black holes feeding off companion stars — a process called accretion. They also are suspected to be the long-sought-after “medium-sized” black holes – missing links between smaller, stellar-size black holes and the gargantuan ones that dominate the hearts of most galaxies. But research into the true nature of ULXs continues toward more definitive answers.”  

“We took it for granted that the powerful ULXs must be massive black holes,” said lead study author Matteo Bachetti, of the University of Toulouse in France. “When we first saw the pulsations in the data, we thought they must be from another source.”  

“Having a diverse array of telescopes in space means that they can help each other out,” said Paul Hertz, director of NASA’s astrophysics division in Washington. “When one telescope makes a discovery, others with complementary capabilities can be called in to investigate it at different wavelengths.”  

What’s next?

Space scientists will now use NASA’s complete array of astronomical equipment and spacecraft to look at how this dead star is able to radiate x-rays so intensely. Plans are for NuSTAR, the Swift Gamma-ray Burst Explorer, and Chandra X-ray Space Observatory to have a look at the weird behavior of M82 X-2.  

They’ll also start looking at other ULXs to see if they can find anymore that are pulsars, rather than a binary star system with an accreting black hole. This research could open a window of discovery on the true nature and origin of these energetic and enigmatic celestial objects.  

Visit here for more information about NuSTAR.

Visit here to learn more about the Chandra X-ray Observatory.

Look here for more information concerning the Swift Gamma-ray Burst Explorer.

Visit here for more on the XMM-Newton Observatory.

You can find more information on the Hubble Space Telescope here.

You can find more information on all NASA missions here.

Read about methane clouds traveling over the north seas of Saturn’s moon Titan

Discover Einstein’s spacetime

Read about the meteorite that lit up the skies over Russia