Galactic X-ray emissions originate from stars

May 05, 2009
The plane of the Milky Way, recorded with the Chandra satellite in three colours: Photons with energies between 0.5 and 1keV appear red, those between 1 and 3keV green, and those between 3 and 7keV blue. Discrete sources are indicated by circles. Image: Mikhail Revnivtsev

( -- A 25-year old astronomical mystery has been solved: Most of the diffuse X-ray emissions in the Milky Way do not originate from one single source but from so-called white dwarfs and from stars with active outer gas layers. Mikhail Revnivtsev from the Excellence Cluster Universe at the TU Munich and his colleagues at the Max Planck Institute for Astrophysics in Garching, the Space Research Institute in Moscow and the Harvard-Smithsonian Center for Astrophysics in Cambridge have now succeeded in proving this.

It is now 25 years since scientists discovered diffuse X-ray emissions from the vicinity of the plane. Since then, a whole generation of astronomers has been racking its brains as to their origin. Energetic X-ray emissions usually originate from very hot gases in a temperature range between 10 and 100 million degrees Celsius. And this "Galactic Ridge X-ray Emission" (GRXE) is also typical for very hot, optically thin plasma.

A gas with these thermal properties would, however, immediately escape from our galaxy - the Milky Way would continuously lose colossal amounts of energy and finally collapse as the existing energy sources, such as stars and supernovae, would not be sufficient to replenish such a loss. Cosmic particles colliding with the interstellar medium could also be ruled out as an explanation for the GRXE.

It is only recently that observations with the RXTE and Integral satellites have shown that the X-ray emissions of the Milky Way exhibit the same distribution pattern as the stars. Since then, it has been assumed that a large portion of the GRXE originates from individual stars. These findings motivated the international team to carry out more precise measurements with the Chandra X-ray telescope. The test area chosen was a small celestial region near the centre of the Milky Way.

The region chosen, about half as big as a , lent itself to the observations for two reasons: On the one hand because of the high GRXE intensity, which minimized the "interfering radiation" from extra-galactic X-ray sources; and on the other hand because the interstellar matter at this position absorbs only small amounts of radiation so that it was even possible to detect weak discrete sources with Chandra.

Chandra actually managed to identify 473 point sources of X-rays in a sector of the search field covering only 2.6 arcminutes. In a further step, the group used measurements from the Spitzer satellite observatory to prove that the results of the sector observed could be applied to the whole galaxy.

Most of the 473 X-ray sources are probably white dwarfs, which accrete matter from their surroundings, as well as stars with high activity in their outermost gas layer, the corona. White dwarfs are the remnants of extinct, low-mass suns. These cooling dead stars frequently orbit a partner, and in such a binary star system the white dwarf extracts matter from its larger partner until it becomes a Type Ia supernova.

The resolution of the diffuse X-ray emissions in our galaxy into discrete sources has far-reaching consequences for our understanding of a number of astrophysical phenomena. Astronomers can use the GRX emission as a calibration for the spatial distribution of star populations within the Milky Way, for example. The results were also relevant for research into other galaxies: It now seems clear that the diffuse X-ray radiation from these objects originates from and active .
Original work:

More information: Mikhail Revnivtsev, Sergey Sazonov, Eugene Churazov, William Forman, Alexey Vikhlinin and Rashid Sunyaev, Discrete sources as the origin of the Galactic X-ray ridge emission, Nature, Vol. 458, No. 7242, April 30, 2009

Provided by Max-Planck-Institute

Explore further: Can astronomy explain the biblical Star of Bethlehem?

add to favorites email to friend print save as pdf

Related Stories

Resolving a galactic mystery

Apr 29, 2009

An extremely deep Chandra X-ray Observatory image of a region near the center of our Galaxy has resolved a long-standing mystery about an X-ray glow along the plane of the Galaxy. The glow in the region covered ...

Origin of Galactic X-rays Explained

Feb 21, 2006

New Map of the Milky Way Reveals Millions of Unseen Objects Using the most sensitive X-ray map of the Galaxy, obtained combining 10 years of data of Rossi XTE orbital observatory, scientists from the Max Plan ...

Chandra Lifts the Veil on Milky Way 'Hotspot'

Jan 23, 2008

NASA's Chandra X-ray Observatory is helping to demystify Westerlund 2, a young star cluster with an estimated age of about one- or two-million years. Heavily obscured by dust and gas, Westerlund 2 has been ...

Galactic X-ray background source is found

Feb 23, 2006

Scientists at the Max Planck Institute for Astrophysics in Germany say they've found the origin of galactic background emissions -- white dwarf stars.

Integral sees the Galactic centre playing hide and seek

Jan 18, 2007

ESA's gamma ray observatory Integral has caught the centre of our galaxy in a moment of rare quiet. A handful of the most energetic high-energy sources surrounding the black hole at the centre of the Galaxy ...

Integral: Three Years Of Insight Into The Violent Cosmos

Oct 24, 2005

Observing the cosmos, full of violent phenomena and extreme energy, has been the task of ESA's Integral gamma-ray observatory since its launch on 17 October 2002. Three years later, the mission is going very well and has ...

Recommended for you

Can astronomy explain the biblical Star of Bethlehem?

Dec 24, 2014

Bright stars top Christmas trees in Christian homes around much of the world. The faithful sing about the Star of Wonder that guided the wise men to a manger in the little town of Bethlehem, where Jesus was ...

Hubbles spies the beautiful galaxy IC 335

Dec 24, 2014

This new NASA/ESA Hubble Space Telescope image shows the galaxy IC 335 in front of a backdrop of distant galaxies. IC 335 is part of a galaxy group containing three other galaxies, and located in the Fornax ...

Image: Multicoloured view of supernova remnant

Dec 22, 2014

Most celestial events unfold over thousands of years or more, making it impossible to follow their evolution on human timescales. Supernovas are notable exceptions, the powerful stellar explosions that make ...

Ultra-luminous X-ray sources in starburst galaxies

Dec 22, 2014

Ultra-luminous X-ray sources (ULXs) are point sources in the sky that are so bright in X-rays that each emits more radiation than a million suns emit at all wavelengths. ULXs are rare. Most galaxies (including ...

When a bright light fades

Dec 22, 2014

Astronomer Charles Telesco is primarily interested in the creation of planets and stars. So, when the University of Florida's giant telescope was pointed at a star undergoing a magnificent and explosive death, ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet May 06, 2009
wonder how much x-ray energy is outputted from our local Sol, enough to support the earth and then some i figure, x-ray solar panels?
not rated yet May 06, 2009
"sender" has a point! The COMPLETE solar spectrum could yield about all the energy we need! The x-ray
portion is just enough to provide a good part of
our "cancer" needs! It's U.V. plus man-made radiology provides most of the rest!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.