The familiar Whirlpool Galaxy (M51) assumes an alien appearance photographed by the orbiting Chandra telescope in x-rays. The bright points are x-ray binaries, pairs of stars where either a compact neutron star or black hole is capturing material from a close companion star. At right is a visible light picture of the galaxy. Credit: ASA/CXC/Wesleyan Univ./R.Kilgard /Right: Jim Misti
Ever wish you had x-ray vision? NASA’s Chandra X-Ray Observatory does and used it to make this eerie, new view of the famous Whirlpool Galaxy in Hunting Dogs constellation. Gone are the familiar whirls of stars that shape its spiral arms, replaced by glittering points of x-ray light from matter swirling down black holes. The blobby purple stuff is gas that’s been super-heated by massive stars that have erupted as supernovae.
900,000 seconds of observing time went into creating the photo which sparkles with nearly 500 x-ray sources. Previous exposures revealed only about 100. Most are found within the Whirlpool’s disk but some are between us and the galaxy or behind it.
This combined image Chandra’s view (purple) along with optical data from the Hubble Space Telescope (red, green, and blue). Researchers are studying the XRBs in M51 to better understand the role they play in the evolution of the galaxy. The galaxy is located 30 million light years away in Canes Venatici the Hunting Dogs near the end of the handle of the Big Dipper. Credit: X-ray: NASA/CXC/Wesleyan Univ./R.Kilgard, et al; Optical: NASA/STScI
Most of the x-ray point are x-ray binaries (XRBs) or very close ‘double stars’ where one of the components is either a compact city-sized star called a neutron star or a black hole. When a massive star explodes as a supernova it can leave behind either it’s much compressed core – now a neutron star – or a black hole.
Artist’s view of a normal star losing matter to a compact star – either neutron star or black hole – in an x-ray binary. Gas is funneled into a disk, gets heated and emits x-rays and other forms of light until it disappears down the hole or adds to the mass of the neutron star. Credit: ESO /. L. Cacada
Matter from the companion star is pulled and accelerated by the intense gravitational field of the compact star and heated to millions of degrees, producing a luminous X-ray source. Picture water going down your bathtub drain so quickly it heats up to a million degrees to produce beams of x-rays.
The Chandra observations reveal that at least ten of the XRBs in the galaxy are bright enough to contain black holes. In eight of these systems the black holes are likely capturing material from companion stars that are much more massive than the Sun.
Astronomers have been using Chandra to observe black hole XRBs in the Whirlpool for some ten years. During that time, the sources have remained consistently bright. Giant stars release a steady stream of material in stellar winds, while their black hole companions are only too happy to gobble up the gas and steal it away from the universe forever.
High-mass X-ray binary systems (red stars) are superimposed on an artist’s impression of the Milky Way galaxy. The yellow star shows the position of the Sun. Credit: A. Coleiro and S. Chaty; Image of spiral arms: NASA/Adler/U. Chicago/Wesleyan/JPL-Caltech
The Whirlpool’s in the process of merging with its companion galaxy NGC 5195 (upper left in photos). While no individual stars are ‘harmed’ in these mergers, gas clouds collide and trigger waves of fresh star formation. Some of these stars are supergiants that zip through their lifetimes in a few million years (compared to several billions for stars like our sun) and explode as supernova, leaving remnant compact stars behind, including XRBs.
Those paired up with other suns will detonate as supernovae to create a new x-ray binaries. Most of the XRBs containing black holes in M51 are located close to regions where stars are forming, showing their connection to the oncoming galactic collision. Our own galaxy has its own assortment of XRBs which help astronomers trace out its spiral arms, where most of the new stars are forming in the galaxy.
