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Astronomers discover the first exoplanet in another galaxy

Astronomers discover the first exoplanet in another galaxy

Updated Oct 29, 2021 at 12:44 PM

  • Do planets orbit stars in other galaxies?
  • This question can now be answered with a very high probability of yes.
  • Astronomers have detected direct evidence of this in their data for the first time.

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The Vortex Galaxy (M51) is a fascinating sight—and now it has revealed one of its secrets: Astronomers working with Rosanne Di Stefano of the Center for Astrophysics at the Harvard and Smithsonian Center for Astrophysics in Cambridge, Massachusetts, have for the first time discovered direct evidence that a cosmic object in a galaxy one planets circled. The findings could open a new window for searching for exoplanets at very great distances, NASA reports.

The researchers made use of the Romanian-American authority’s Chandra X-ray Observatory. Specifically, they examined a candidate exoplanet in a binary system called M51-ULS-1, which is located in the Whirlpool Galaxy. A binary star system contains a black hole or neutron star orbiting a companion star that has a mass about 20 times the mass of the Sun. But there is something else in orbit around a black hole or neutron star: an exoplanet roughly the size of Saturn.

The X-ray image (left) shows the region in the Whirlpool Galaxy in which an exoplanet was discovered. The artist’s rendering of the binary system can be seen on the right.

© NASA/CXC/SAO/R. Distefano et al./ESA/STScI/Grendler/M. Weiss

This is how the search for exoplanets works

The method used for discovery works in a similar way to how it is usually used to search for exoplanets in our Milky Way: If an exoplanet moves in front of its parent star during a so-called transit, the star becomes slightly darker when viewed from Earth. This process is roughly comparable to a partial solar eclipse on Earth, but it is much weaker. Special telescopes can detect these small fluctuations in light.

The research team led by Di Stefano has now altered the spectrum for their investigations: Instead of searching in the optical range of light, the astronomers looked for breaks in the X-ray range of electromagnetic radiation — particularly in binary systems.

X-ray transit allows discoveries to be made at a much greater distance

These glowing systems typically contain a neutron star or black hole that attracts gas from a nearby companion star orbiting it. Matter near a neutron star or black hole gets hot and glows in the X-ray spectrum. Because the region that produces bright X-rays is small, any planet passing in front of it will block most or all of the X-rays. This makes crossing easier to see.

Method advantage: Operate over very long distances. “We are trying to open a new window to search for other worlds by searching for candidate planets in the X-ray wavelength range. This is a strategy that enables us to detect such objects in other galaxies,” Di Stefano explains. So far, astronomers have found all known exoplanets and candidate exoplanets in the Milky Way, almost all less than 3,000 light-years from Earth. An exoplanet in M51 would be about 28 million light-years away. That would be a quantum leap if the results are confirmed.

The results have not yet been confirmed

More data is needed to determine if this is indeed an exoplanet in M51. However, there is still one problem with this: the large orbit of the filter. At the moment, he doesn’t seem to be wandering in front of his partner in about 70 years, which is a problem, notes co-author Nia Imara of the University of California, Santa Cruz, “To confirm that we unfortunately, see the planet will have to wait decades to see another transit. But because of the lack of Certainty about how long the orbit will take, we don’t know exactly when to look.”

But until this problem is resolved, astronomers won’t be idle: they’ll be searching archive data from Chandra and the Esa XMM Newton Observatory in search of more candidate exoplanets in other galaxies. Extensive data sets are available for at least 20 galaxies, offering the potential for new discoveries.

Sources used:

  • NASA: The first evidence of a planet identified outside our galaxy
  • Nature astronomy: A potential candidate planet in an outer galaxy discovered by X-ray transit

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