Chandra telescope measures X-ray environment in Alpha Centauri system

Levels of stellar radiation can determine whether planets in stars' habitable zones are actually habitable.
By Laurel Kornfeld | Jun 11, 2018
NASA's Chandra X-ray Observatory has measured X-ray levels in the Alpha Centauri system, the nearest star system to our Sun, located about four light years away.

Bombardment by high levels of X-rays from a host star can render a planet uninhabitable to life as we know it even if that planet is located in its star's habitable zone, where temperatures allow liquid water to flow on the surface.

Comprised of three stars, Alpha Centauri A, Alpha Centauri B, and Alpha Centauri C or Proxima Centauri, the system has been monitored by Chandra for more than ten years.

The system's two bright stars, Alpha Centauri A and B, which orbit close to one another, are not emitting the high levels of radiation that would strip away the atmospheres of any planets orbiting them.

Alpha Centauri A is considered to be a twin of our Sun, with both being approximately the same age and mass and having the same levels of brightness.

While Alpha Centauri B is somewhat smaller and dimmer than its companion, it, too is considered Sun-like.

Proxima Centauri, the system's third star, and the only one where an orbiting planet has been discovered, is a much smaller red dwarf star in a distant orbit around both its larger companions. It is more than 10,000 times further from the system's other two stars than the Earth is from our Sun.

Red dwarf stars like Proxima emit high levels of radiation that bombard their planets, often leaving them uninhabitable.

The planet found orbiting Proxima is Earth-like. To date, astronomers have not found any planets orbiting Alpha Centauri A or B. This could be due to the two orbiting very close together over the last ten years, with their combined brightness making it more difficult to detect planets around them.

"Because it is relatively close, the Alpha Centauri system is seen by many as the best candidate to explore for signs of life," explained Tom Ayres of the University of Colorado at Boulder. "The question is, will we find planets in an environment conducive to life as we know it?"

As the only X-ray telescope capable of resolving Alpha Centauri A and B, Chandra is the ideal instrument for studying this system.

Having studied the cycles of X-ray activity in the system's stars approximately every six months since 2005, Chandra found that any planets in Alpha Centauri A's habitable zone receive less stellar radiation than Earth does from the Sun.

Planets in the habitable zone of Alpha Centauri B receive slightly more radiation from the star than Earth does from the Sun, but these levels are not sufficient to affect its habitability.

Proxima's habitable zone receives 500 times more radiation than Earth does from the Sun, and this amount can spike to 50,000 times more during a stellar flare.

The study's findings, published in the journal Research Notes of the American Astronomical Society (AAS), were presented at the 232nd meeting of the AAS in Denver, Colorado, during the first week in June.



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