When NASA's Transiting Exoplanet Survey Satellite launched into space in April 2018, it had a specific goal: to search the universe for new planets.
In a recent study, a team of astronomers at Ohio State University showed that the survey, nicknamed TESS, can also be used to monitor a specific type of supernova to give scientists more clues as to what the explosion of caused white dwarf stars ̵
"We've known for years that these stars are exploding, but we have terrible ideas about why they explode," said Patrick Vallely, lead author of the study and graduate of Ohio State University's Astronomy. "The big thing here is that we can show that this supernova is incompatible with a white dwarf exploding directly from a standard star companion in it – a standard idea that has made people try it have to find hydrogen signatures because the TESS light curve shows no evidence of the explosion on the surface of a companion and because the hydrogen signatures in the SALT spectra do not evolve like the other elements we can rule out this standard model. "
listed in the Monthly Notices of the Royal Astronomical Society are the first published results of a supernova observed with TESS and provide new insights into long-held theories of the elements left behind after a white dwarf star in a supernova explodes.
These elements have long troubled astronomers Astronomers believe that the mass of a companion star in the vicinity increases and becomes too large to remain stable. But if that's the case, then, as the astronomers suspected, the explosion should leave trace elements of hydrogen, a crucial building block of stars and the entire universe. (White dwarf stars have by nature already burned their own hydrogen and would therefore not be a source of hydrogen in a supernova.)
But up to this TESS-based observation of a supernova, astronomers had never seen this hydrogen after the explosion: this supernova is the first of its kind, in which astronomers have measured hydrogen. First reported by a team of Carnegie Institution for Science observatories, this hydrogen could change the nature of what astronomers know about white dwarf supernovae.
"The most interesting thing about this particular supernova is the hydrogen we've seen in its spectra (the elements that leaves the blast)," said Vallely. "For years, we've searched for hydrogen and helium in the spectra of this type of supernova – these elements help us understand what the supernova actually caused."
The hydrogen could mean that the white dwarf is a star consumed nearby , In this scenario, the second star would be a normal star in the middle of its lifetime – not a second white dwarf. When the astronomers measured the light curve of this supernova, the curve showed that the second star was actually a second white dwarf. Where does the hydrogen come from?
Professor of Astronomy Kris Stanek, Vallely's Ohio consultant and co-author of this paper, said it was possible that the hydrogen came from a companion star – a normal star. but he thinks it's more likely that the hydrogen came from a third star, which happened to be near the exploding white dwarf and was consumed in the supernova.
"We would think that because we see this hydrogen, it means that the white dwarf consumed a second star and exploded, but due to the light curve we saw from this supernova, that might not be true," said Stanek.
"Due to the light curve, it's most likely that we made it. I think the hydrogen could come from a third star in the system," Stanek added. "The prevailing scenario, at least in Ohio State, is that the way to make a supernova of type Ia (pronounced 1-A) is for two white dwarf stars to interact – even collide – but also for a third star to deliver the hydrogen. "
For Ohio State research, Vallely, Stanek, and a team of astronomers from around the world combined data from TESS, a 10-centimeter-diameter telescope, with All-Sky Automated Survey for Supernova data (ASAS) -SN.) ASAS-SN is run by the US state of Ohio and consists of small telescopes around the world, which search the sky for supernovae in distant galaxies.
TESS, in comparison, was designed to search the sky for planets in our nearby galaxy – and to provide data much faster than previous satellite telescopes. This means that the Ohio State team was able to use data from TESS to see what happened in the first moments after the explosion around the supernova – an unprecedented opportunity.
The team combined data from TESS and ASAS-SN with data from the South African Large Telescope to evaluate the post-supernova elements. There they found both hydrogen and helium, two signs that the exploding star had consumed a companion star nearby. "And this supernova is the first exciting case of this synergy."
The supernova that watched this team was a Type Ia, a type of supernova that can occur when two stars orbit each other – which astronomers call a binary system. In some cases of a type I supernova, one of these stars is a white dwarf.
A white dwarf has burned off all its nuclear fuel leaving only a very hot core. (White dwarf temperatures exceed 100,000 degrees Kelvin – nearly 200,000 degrees Fahrenheit.) If the star does not grow larger by stealing energy and matter from nearby stars, the White Dwarf spends billions of years cooling down before he turns into a lump of black carbon.
When the White Dwarf and another star are in a binary system, the White Dwarf slowly picks up mass from the other star until the White Dwarf finally explodes into a supernova.
Type I supernovae are important for space science – They help astronomers measure distances in space and calculate how fast the universe expands (a discovery so important that in 2011 it won the Nobel Prize for Physics) received).
"These are the most famous types of supernova and they have led to the discovery of dark energy in the 1990s," said Vallely. "They are responsible for the existence of so many elements in the universe, but we do not understand the physics behind it so well, and that's exactly what I like when I combine TESS and ASAS-SN here so we can build that." Data and use them to find out a little more about these supernovae.
Scientists largely agree that the companion star leads to a supernova of the white dwarf, but the mechanism of this explosion and the composition of the companion star are less clear.
This discovery, Stanek said, provides some evidence that the companion star in this type of supernova is probably another white dwarf.
"We see something new in these data and this helps our understanding of the Ia-supernova phenomenon," he said. "And we can explain all this with the scenarios we already have – we just have to let the third star in this case be the source of hydrogen. "
Three out-of-control stars are considered survivors of thermonuclear explosions
P.J. Vallely et al. ASASSN-18tb: a highly unusual type Ia supernova observed by TESS and SALT Monthly Notices of the Royal Astronomical Society (2019). DOI: 10.1093 / mnras / stz1445
Supernova observation first with NASA satellite (2019, July 16)
retrieved on 16 July 2019
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