The European Southern Observatory's Very Large Telescope (ESO's VLT) has
captured an image of a planet orbiting b Centauri, a two-star system that
can be seen with the naked eye. This is the hottest and most massive
planet-hosting star system found to date, and the planet was spotted
orbiting it at 100 times the distance Jupiter orbits the Sun. Some
astronomers believed planets could not exist around stars this massive and
this hot—until now.
"Finding a planet around b Centauri was very exciting since it completely
changes the picture about massive stars as planet hosts," explains Markus
Janson, an astronomer at Stockholm University, Sweden and first author of
the new study published online today in Nature.
Located approximately 325 light-years away in the constellation Centaurus,
the b Centauri two-star system (also known as HIP 71865) has at least six
times the mass of the Sun, making it by far the most massive system around
which a planet has been confirmed. Until now, no planets had been spotted
around a star more than three times as massive as the Sun.
Most massive stars are also very hot, and this system is no exception: its
main star is a so-called B-type star that is over three times as hot as the
Sun. Owing to its intense temperature, it emits large amounts of ultraviolet
and X-ray radiation.
The large mass and the heat from this type of star have a strong impact on
the surrounding gas, that should work against planet formation. In
particular, the hotter a star is, the more high-energy radiation it
produces, which causes the surrounding material to evaporate faster. "B-type
stars are generally considered as quite destructive and dangerous
environments, so it was believed that it should be exceedingly difficult to
form large planets around them," Janson says.
But the new discovery shows planets can in fact form in such severe star
systems. "The planet in b Centauri is an alien world in an environment that
is completely different from what we experience here on Earth and in our
Solar System," explains co-author Gayathri Viswanath, a Ph.D. student at
Stockholm University. "It's a harsh environment, dominated by extreme
radiation, where everything is on a gigantic scale: the stars are bigger,
the planet is bigger, the distances are bigger."
Indeed, the planet discovered, named b Centauri (AB)b or b Centauri b, is
also extreme. It is 10 times as massive as Jupiter, making it one of the
most massive planets ever found. Moreover, it moves around the star system
in one of the widest orbits yet discovered, at a distance a staggering 100
times greater than the distance of Jupiter from the Sun. This large distance
from the central pair of stars could be key to the planet's survival.
These results were made possible thanks to the sophisticated
Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE)
mounted on ESO's VLT in Chile. SPHERE has successfully imaged several
planets orbiting stars other than the Sun before, including taking the first
ever-image of two planets orbiting a Sun-like star.
However, SPHERE was not the first instrument to image this planet. As part
of their study, the team looked into archival data on the b Centauri system
and discovered that the planet had actually been imaged more than 20 years
ago by the ESO 3.6-m telescope, though it was not recognized as a planet at
the time.
With ESO's Extremely Large Telescope (ELT), due to start observations later
this decade, and with upgrades to the VLT, astronomers may be able to unveil
more about this planet's formation and features. "It will be an intriguing
task to try to figure out how it might have formed, which is a mystery at
the moment," concludes Janson.
This research was presented in a paper tilted "A wide-orbit giant planet in
the high-mass b Centauri binary system" to appear in Nature.
Reference:
Markus Janson, A wide-orbit giant planet in the high-mass b Centauri binary
system, Nature (2021).
DOI: 10.1038/s41586-021-04124-8.
No comments:
Post a Comment