Be my X-ray valentine

X-ray: NASA /CXC /MIT / S.Rappaport et al, Optical: NASA / STScI

This image shows Arp 147, a pair of interacting galaxies some 430 million light years from Earth, as seen by the Chandra X-ray Observatory and the Hubble Space Telescope. The ring-shaped object on the right is a remnant of a spiral galaxy that collided with the elliptical galaxy to the left millions of years ago.



By John Roach

Here’s a piece of eye candy to share with your honey this Valentine’s Day: a colorful ring of stars encrusted with black holes that cast a pink glow, thanks to a little creative image processing.

The pink areas represent X-ray emissions detected by NASA’s Chandra X-ray Observatory. Visible-light readings from the Hubble Space Telescope give the ring its red, green, and blue colors.

So what are we actually seeing? This is a pair of interacting galaxies known as Arp 147, located about 430 million light-years from Earth in the constellation Cetus. The unusual arrangement was formed when the remnant spiral galaxy (right) collided with the elliptical galaxy on the left. The collision produced an expanding wave of star formation that shows up here as a blue ring containing an abundance of massive young stars. These stars race through their evolution in a few million years and explode as supernovae, leaving behind neutron stars and black holes, as explained in a Chandra image advisory.

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Some of these neutron stars and black holes have companion stars and can become bright X-ray sources as they pull in matter from these companions. The nine X-ray sources scattered around the ring in Arp 147 are so bright that they must be black holes, with masses likely 10 to 20 times that of the sun.

X-ray: NASA /CXC /MIT / S.Rappaport et al, Optical: NASA / STScI

This composite image of Arp 147 shows Chandra X-ray data in pink, Hubble optical data in red, green and blue, ultraviolet GALEX data in green and infrared Spitzer data in red

The image also shows an X-ray source in what astronomers believe is a poorly fed supermassive black hole in the center of the red galaxy. Other objects in the image include a foreground star (visible at lower left) and a background quasar (seen as the pink source above and to the left of the reddish galaxy).

Infrared observations of Arp 147 with NASA’s Spitzer Space Telescope and ultraviolet observations with NASA’s Galaxy Evolution Explorer allowed astronomers to estimate the rate of star formation in the ring. According to their calculations, the most intense star formation ended about 15 million years ago in Earth’s time frame.

The findings appeared in the Oct. 1 issue of The Astrophysical Journal.

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John Roach is a contributing writer for Connect with the Cosmic Log community by hitting the “like” button on the Cosmic Log Facebook page or following’s science editor, Alan Boyle, on Twitter (@b0yle).


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