Exoplanets are planets found outside of our Solar System.
Scientists may have finally discovered a planet in another galaxy for the first time in history.
Using NASA's Chandra X-ray Observatory, this exciting result opens a new opportunity for
searching for exoplanets outside the Milky Way and beyond.
Until now, astronomers have discovered all known exoplanets and exoplanet candidates
in the Milky Way galaxy, nearly all of them within 3,000 light-years from Earth.
The possible exoplanet, called M51-ULS-1b, is located 28 million light-years away in
Messier 51 (M51), widely known as the Whirlpool galaxy.
This discovery could be the tip of the iceberg, leading to the discovery of many more exoplanets
beyond the Milky Way.
Astronomers examined three galaxies beyond the Milky Way using NASA's Chandra X-ray Observatory
and the European Space Agency's XMM-Newton space telescope.
They studied 55 different systems in M-51, the Whirlpool galaxy, 64 systems in Messier
101 (M-101), also known as the "Pinwheel galaxy," and 119 systems in Messier 104, also known
as the "Sombrero galaxy."
Scientists are attempting to break new ground in the search for other worlds by looking
for planet candidates at X-ray wavelengths, an approach that makes it possible to discover
them in other galaxies.
The object in M-51 was discovered using transits, which occur when an object passes in front
of a star.
When it does this, some of the star's light is blocked, resulting in a brief dip in brightness.
Thousands of exoplanets, or planets outside our solar system, have been discovered using
this method in the past (but still in our galaxy).
Astronomers have searched for dips in optical light, electromagnetic radiation that humans
can see, using both ground-based and space-based observatories, such as those on NASA's Kepler
and TESS missions.
This has led to the discovery of thousands of planets.
To spot the planet, the team led by Dr. Di Stefano instead used Chandra to hunt for dips
in the brightness of X-rays received from the X-ray bright binary systems.
These luminous systems contain a neutron star or black hole that pulls gas from a closely
orbiting companion star.
The material near the neutron star or black hole becomes superheated and glows in X-rays.
Because the area producing bright X-rays is small, planets passing in front of those stars
could actually block out those X-ray emissions entirely, making the transit easier to identify.
This could allow exoplanets to be discovered at considerably greater distances than existing
optical light transit studies, which must be able to detect minute changes in light
since the planet only blocks a portion of the star.
The researchers used this method to find an exoplanet candidate in M51-ULS-1, a binary
system in the Whirlpool galaxy.
The binary star system contains two massive objects, either a neutron star or a black
hole, which orbits a companion star with a mass of nearly 20 times that of the Sun.
The X-ray transit they witnessed lasted a total of about three hours, and the X-ray
emissions dipped all the way to zero.
Based on this and other data, the researchers believe that the exoplanet candidate is around
the size of Saturn and orbits the neutron star or black hole at nearly twice the distance
of Saturn from the Sun.
This research could be the first to confirm the existence of a planet in another galaxy,
perhaps ushering in a new era of planet discovery and study.
However, these findings do not yet prove that the object observed by Chandra in this study
is a planet.
To confirm this assertion, more data needs to be gathered.
The object won't pass in front of its star for another 70 years, so astronomers won't
be able to observe it again for a long time.
Could the dimming have been caused by a cloud of gas and dust passing in front of the X-ray
source?
It is possible but exceedingly unlikely.
Despite this, the team has stated that they expect other scientists to examine the data
they've gathered and the findings they've made.
This could help them confirm what they've found and advance the research further, despite
the time left until the next transit.
According to Dr. Di Stefano, the new generation of optical and infrared telescopes will not
be able to compensate for the problems of crowding and dimness, so X-ray observations
will likely remain the primary method for detecting planets in other galaxies.
However, she did mention that a technique known as microlensing could be helpful in
identifying extra-galactic planets.
Finally, another intriguing area of research is looking for X-ray transits in the Milky
Way X-ray sources in order to find new nearby planets in strange surroundings.