Chandra Observatory may have discovered extra-galactic planet
An artist’s conception of an extra-galactic planet transiting a binary star system consisting of a Sun-like star and a neutron star or black hole. NASA’s Chandra X-ray Observatory may have found evidence for the first-ever known extra-galactic planet. Credit: NASA/CXC/M. Weiss
Scientists using NASA’s Chandra X-ray Observatory may have found evidence for the first-ever known extra-galactic planet, located 28 million light years away in the Whirlpool Galaxy, also known as Messier 51 (M51).
The detection was made indirectly by observation of what appeared to be a planet passing in front of a binary star system composed of a Sun-like star and a companion that is either a neutron star or black hole.
Neutron stars and stellar-mass black holes are remnants of massive stars that ended their lives in supernova explosions. If this planet does exist, it would have had to survive a supernova explosion and the resulting radiation produced by it.
A composite image of the Whirlpool Galaxy created with X-ray images from Chandra and optical images taken by the Hubble Space Telescope. The box insert shows the location of the possible planet. Credit: X-ray: NASA/CXC/SAO/R. DiStefano, et al.; Optical: NASA/ESA/STScI/Grendler
Chandra is an X-ray observatory. The science team that observed the possible planet measured a dimming of X-rays coming from the binary system, which has been designated M51-ULS-1. For a binary star system to emit X-rays, one of its stars must be a neutron star or black hole.
X-ray transits are easier to detect than those in other wavelengths, even at great distances, because the regions that produce the X-rays are small. This means the X-rays completely disappear if an object transits, or passes in front of, their source. In the case of M51-ULS-1, the X-ray emission decreased to almost nothing for a total of three hours.
More than 4,500 exoplanets have been discovered over the last 30 years, but all are located within the Milky Way Galaxy, and most of those are located within 3,000 light years of Earth.
Many were discovered by NASA’s Kepler and Transiting Exoplanet Survey Satellite (TESS) missions, which also used the transit method but did so in optical light.
If this extra-galactic planet exists, scientists estimate it is approximately the size of Saturn and orbits the neutron star or black hole at twice the distance Saturn orbits the Sun.
Because the planet has such a long orbit, scientists will not be able to observe another transit — the usual method of verifying that a detected transit is real — for at least 70 years.
“Unfortunately, to confirm that we’re seeing a planet, we would likely have to wait decades to see another transit. And because of the uncertainties about how long it takes to orbit, we wouldn’t know exactly when to look,” said Nia Imara of the University of California at Santa Cruz, a co-author of a paper on the findings published in the journal Nature Astronomy.
Led by Rosanne DiStefano of the Harvard Smithsonian Center for Astrophysics (CfA), the science team looked at 55 systems in three other galaxies for similar X-ray transits using both Chandra and the European Space Agency‘s (ESA) XMM-Newton telescopes. To date, none were found.
They also plan to look through archival data from both observatories, which covers more than 20 galaxies, for similar X-ray transits.
“We are trying to open a whole new arena for finding other worlds by searching for planet candidates at X-ray wavelengths, a strategy that makes it possible to discover them in other galaxies,” DiStefano said.
Video courtesy of SciTech Daily
Laurel Kornfeld
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.
