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Author: Monica Young
Translation: He Yuying
Proofreader: Zhu Chenyu
Review: Pastor Proofreading Group
Arrangement: Tao Banghui
Backstage: Kutriya Fuka, Li Ziqi, Hu Yongwei, Dong Tengchen
Original link: https://skyandtelescope.org/astronomy-news/did-we-find-a-planet-in-another-galaxy/
In a revolutionary way, astronomers have actually detected a signal from a so-called "extrasolar planet," but it's still a conundrum to confirm that it's true.
We have planets all over the galaxy: even counting the thousands of vaguely looking "candidate stars," we've found about 5,000 planets so far. Such a sufficient number of planets also exists in other galaxies, and because of the distance, our existing technical means are usually undetectable.
And now, a team of astronomers led by Rosan Di Stefano of Harvard University and the Center for Astrophysics at the Smithsonian Institution has found a planet that is likely to be extragalactic, or as they call it, an "extragalactic planet," and the results have been published in Nature-Astronomy. But even if it does exist, its location is rather sinister: next to a black hole. Specifically, the candidate planet orbits an X-ray-emitting binary system (XRBS), one of which could be a black hole or neutron star, pumping material from its own companion star.
It's possible that a planet in a spiral galaxy passes through a black hole 28 million light-years away. The black hole sucks up material from a bright, massive companion star that gets hot as it moves into the black hole. The planet briefly blocks the relatively small X-ray emission region closest to the black hole.
It's possible that a planet in a spiral galaxy passes through a black hole 28 million light-years away. The black hole sucks up material from a bright, massive companion star that gets hot as it moves into the black hole. The planet briefly blocks the relatively small X-ray emission region closest to the black hole.
Searching for exoplanets in such places sounds a bit strange, but then again, the first exoplanet 1 discovered so far orbits a dense star (pulsar)2, rather than an ordinary star.
The key to this method is the relative size of the launch. When stellar material spirals into a black hole, material close to the region near the center heats up and emits X-rays. If a planet passes by here, it blocks most or all of the rays. An Earth-sized planet may block for minutes, and a Jupiter-sized planet may block for hours.
If there is indeed a planet in a spiral galaxy orbiting an X-ray binary system, the image above describes its possible structure. From Earth's perspective, the Saturn-sized planet can block an X-ray emission region with a diameter of 50,000 kilometers for about 3 hours. This orbit is far away, so such a ling will not happen again for a long time.
credit: nasa / cxc / m. weiss
Di Stefano and his team set out to investigate three more recent spiral galaxies for signals from the X-ray-emitting binary star system (XRB). Among them, the vortex galaxy m51 and the windmill galaxy m101 are two forward galaxies, and the other straw hat galaxy m104 is a lateral galaxy.
They've found a treasure in the spiral galaxy. The spiral galaxy is 28 million light-years away, and of that, the bright xrb system, M51-uls-1, looks like a black hole eating away at a huge, bright blue star. Rotating stellar material emits an area of X-rays about 50,000 kilometers wide. The astronomers watched as the light suddenly dimmed tenfold and recovered after three hours.
The occlusion wasn't necessarily caused by the planets, and the team considered other possibilities. But most other causes that can cause this dimming, such as the passage of gas clouds or the interruption of cannibalization when black holes are interrupted, cause some energy to fall earlier or more than others. In contrast, m51-uls-1 is dimmed to the same degree. The object that passes by is also unlikely to be a white dwarf, and its extreme gravity will bend the light, amplifying it rather than obscuring it.
Di Stefano's team experimented with combinations of different sizes and distances to see what kind of combinations matched the sudden dimming they observed, concluding: "This transiting object is likely to be smaller than Jupiter." ”
"The joy and emotion of finding this candidate planet in another galaxy is indescribable, and we researchers have been trying to see more, to discover things that would not have been discovered," Di Stefano said.
The box represents the location of the binary system of X-rays in the spiral galaxy m51, which may possess an exoplanet 28 million light-years from Earth.
x-ray: nasa / cxc / sao / r. distefano, et al.; optical: nasa / esa / stsci / gendler
But don't forget that the object may also be a brown dwarf or a small-mass star. Scott Walker, who was not involved in the study (who is also at the Center for Astrophysics), points out that many massive star systems have not only two stars, but also a third or fourth. If the X-ray-blocking object is a small-mass star in a distant orbit, this is not impossible.
Walker 3 added: "After all, if it were really a planet, it would be too lucky." "The odds of finding a planet in the 2,000 studied light curves are very small, just one in a million.
But Di Stefano noted that we can't yet determine how many XRB systems contain planets there are. If there are actually many such systems, then the one found this time is not "different" at all. "More discoveries are needed to compare our observations and theories," she added, "and I think we'll find them in the next decade." ”
While we don't know if a planet is causing the X-ray dimming, the observations corroborate the theory that Di Stefano and his friends want to use to make more discoveries, not only for our galaxy, but also for other galaxies. "With this approach, we'll learn a lot," she says. ”
Even if we can't get in touch with other galactic civilizations, with Di Stefano's method, we can at least know if there are as many extragalactic planets as we have in our galaxy.
Translator's Note:
[1] First discovery of exoplanets: In 1992 Aleksander Wolszczan and Dale Frail published their discovery of a planet orbiting a pulsar.
[2] Pulsar pulsar: A fast-spinning neutron star with a strong magnetic field of 107–109 t. Short-period pulsed radiation in the millisecond to 100-second range of emission rules is its basic feature. neutron star neutron star: A dense star that relies on the pressure of degenerate neutrons to balance gravity. Compact star compact star: The star's nuclear energy is exhausted, and after gravitational collapse, the internal state of matter plays a dominant role in quantum mechanical effects, with an average density of more than 109 kg/m3 stars. (Quoted above from nadc.china-vo.org)
Compact stars are a general term for white dwarfs, neutron stars, strange stars, black holes and other types of dense objects, the main difference between them and normal stars is that there is no longer nuclear fuel for fusion reactions, thermal pressure is not enough to maintain balance with their own gravity, so they collapse into very small scale, very dense objects. Compact stars are usually the final form of the end of star evolution, and the evolution of stars depends mainly on the mass of the star. In general, stars with masses between 1 and 6 solar masses eventually evolve into white dwarfs, accompanied by mass loss, and their outer shells are ejected outwards, forming planetary nebulae. Stars with a mass of 3 to 8 solar masses evolve into neutron stars, and more massive stars collapse into black holes. (Quoted above from Chinese Wikipedia)
[3] Scott Walker's research also used X-rays, referring to https://www.cfa.harvard.edu/people/scott-j-wolk
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