A Type Ia probably occurs when a white-dwarf star -- the "corpse" of a medium-mass star like the Sun -- is completely blown to bits. Astronomers suspect white dwarfs as the culprits because Type Ia supernovae typically occur in regions of space that contain mostly older stars, suggesting that a Type Ia is the explosion of a long-lived star. Stars that live a long time cannot be particularly massive, adding credence to the white-dwarf theory. And the spectra of Type Ia supernovae show little or no hydrogen, the most common element in the universe.
Instead, they show a lot of carbon and oxygen, which is the composition of a white dwarf. The maximum mass for a white dwarf is 1. White dwarfs of nearly the Chandrasekhar mass are essentially identical, so they undergo nearly identical explosions. The most popular theory for turning a white-dwarf star into a supernova is through an act of stellar cannibalism. If a white dwarf has a close companion star, it might steal gas from the companion's surface.
But just how close would one need to be? Astronomers estimate we have a comfort zone of about 50 light-years. Any supernova closer than that and — well, you get the idea. Usually, the Local Bubble is no cause for concern. But, according to recent estimates, this residual gas could actually magnify the lethal effects of a supernova by increasing the amount of high-energy radiation that reaches Earth. The last time Earth felt the effects of a supernova was about 1.
The explosion took place light-years away — 6. And such a massive star will burn through its fuel quickly, living for only a few million years. Usually massive stars are born in dense clusters, not far off on their own. To actually get so far from its apparent host galaxy, it would have to have been kicked out at a speed far surpassing anything scientists have yet measured.
Oddities Remain A star headed for such a cataclysm is also expected to shed mass over the thousands of years before its death, throwing off material through dense solar winds. And that material is still quite thick and close to the star, implying that it instead shed all that mass in less than 20 years, instead of thousands.
SNiet is one of the best examples of a real-life pair instability supernova, and it also challenges many of the details about how these stars actually look when they explode. Gomez and his team have already been approved for a slot on the Hubble Space Telescope.
Gomez says the observations should be taken within the next six months or so, hopefully answering more questions about this strange star.
Astronomers get a 3D look at nearby stellar nurseries. This may be the first exoplanet found orbiting three stars. Celebrating a century of variable star astronomy. The cannibalistic chaos within planetary systems. Astro for kids : How many stars are there in space? Untangling the Tarantula Nebula, the sky's largest stellar nursery. Breakthrough Starshot: A voyage to the stars within our lifetimes. Massive flare on Proxima Centauri could spell bad news for any alien life.
According to the model, when stars at least 7 to 10 times the mass of our sun go supernova, the blast swallows any inner planets, those orbiting out to several times the distance between Earth and the sun.
Planets orbiting hundreds of times the Earth-sun distance will instead have their orbits disrupted and elongated in such a way that they're eventually flung into interstellar space. In some cases, the disrupted planets will be pushed into more distant but stable orbits around the supernova remnants.
These planets may continue orbiting stellar remnants such as pulsars and even black holes far enough away that they would not be swallowed by their intense gravitational pull—but the survivors would be charred, dead worlds. What's more, these worlds on the edge can easily be stripped off the system and turned rogue by the gravitational pulls of other nearby stars.
In May a different team of astronomers described observational evidence of up to ten planets that appear to be wandering independently through interstellar space. The new expulsion mechanism may account for how those newfound planets escaped their star systems, said Steinn Sigurdsson , an astronomer at Pennsylvania State University not connected to the study. Read a commentary on the paper on Sigurdsson's blog Dynamics of Cats.
But Sigurdsson cautions that there may be another method at play for how planets get kicked out of their star systems. It's even possible the two mechanisms are working together, Sigurdsson added, with the scattering effect putting planets in wider orbits and the supernova then ejecting them from the system. One big question raised by the new study is whether any life could survive expulsion from its planetary clan.
The answer may be yes, if the planet had enough internal heat and already supported subsurface life, said John Debes , a planet hunter not affiliated with Veras' team. Life could also find a way to take hold on planets without host stars under the right conditions, Debes added. There have been studies showing that climatological, geodynamical, and biogeochemical processes might be able to sustain life on starless planets, specifically those with underground oceans with thermal vents, where free-energy flow may still be enough to run a biosphere.
The ultimate goal for Veras and his team would be to actually catch a star in the act of kicking out its planets—which may prove difficult if not impossible.
0コメント