When NASA's Transiting Exoplanet Survey Satellite was launched in space in April 2018, it did so with a specific goal: to seek the universe for new planets.
However, in recently published research, a team of astronomers at Ohio State University showed that the study, called TESS, could also be used to monitor a particular type of supernova, giving scientists more clues about what causes white dwarf stars to explode – and about the elements that these explosions leave.
"We've known this year that these stars are exploding, but we have terrible ideas as to why they explode," says Patrick Vallely, lead author of the study and an Ohio State Astronomy graduate student. "The big thing here is that we can show that this supernova does not correspond to having a white dwarf (take mass) directly from an ordinary star companion and explode in it ̵
Their research, which described in Monthly Messages by the Royal Astronomical Society represents the first published results of a supernova observed with TESS and adds new insights on long-lasting theories of the parts left behind by a white dwarf star exploding into a supernova.
These elements have long troubled astronomers.
A white dwarf explodes into a certain type of supernova, a 1a after hole healing mass from a nearby companion star and grows too large to remain stable, believe astronomers. But if it is true, then the explosion should have theorized theorists, leaving behind hydrogen tissues, a crucial building block of stars and the entire universe. (White dwarf stars have by their very nature already burned through their own hydrogen and that would not be a source of hydrogen in a supernova.) But until this TESS-based observation of a supernova, astronomers had never seen these hydrogen traces in the aftermath of the explosion : This supernova is the first of its kind where astronomers have saturated hydrogen. The hydrogen first reported by a team from the Carnegie Institution for Science observatories could change the type of astronomers who know about white dwarf supernova.
"The most interesting thing about this supernova is the hydrogen we saw in its spectra (the elements that the explosion leaves behind)," Vallely said. "We've been looking for hydrogen and helium in the spectrum of this type of supernova this year – these element helps us understand what caused the supernova in the first place. "
The hydrogen may mean that the white dwarf consumed a nearby star. In that scenario, the other star would be a normal star in the middle of its lifetime – not a second white dwarf. But when astronomers measured the light curve from this supernova, the curve showed that the other star was actually a second white dwarf. So came hydrogen from?
Professor of Astronomy Kris Stanek, Vallely's advisor at Ohio State and a co-author on this paper, said that it is possible that the hydrogen came from a companion – an ordinary, ordinary star – but he believes that it is more likely that the hydrogen came from a third star that happened to be close to the expl the white dwarf and consumed in the supernova by chance.
"We would think that because we see this hydrogen, it means that the white dwarf consumed a second star and exploded, but based on the light curve we saw from this supernova, it may not be true," Stanek says.
"Based on the light curve, the most likely happened, we think, is that hydrogen can come from a third star in the system," Stanek added. "So the current scenario, at least in Ohio State right now, is that the way to do a type Ia (pronounced 1-A) supernova is by having two white dwarf stars interact – even colliding. But also with a third star giving hydrogen. "
For Ohio State Research, Vallely, Stanek, and a team of astronomers from around the world, data from TESS, a 10 cm diameter telescope, was combined with data from the All-Sky Automated Survey for Supernovae (ASAS SN for short). The ASAS-SN is led by Ohio State and consists of small telescopes around the world who see the sky for supernovae in distant galaxies.
In comparison, TESS is intended to search for skies for planets in our nearby galaxy – and to provide data much faster than previous satellite telescopes. That means the Ohio State Team could use TESS data to see what happened around the supernova in the first moments after it exploded – an unrivaled opportunity.
The team combined data from TESS and ASAS-SN with data from the South African large telescope to evaluate the elements that remain in supernovas wake up. They found both hydrogen and helium there, two indicators that the exploding star had somehow consumed a nearby companion star.
"What is really cool about these results is that we can learn new things," Stanek says. . "And this supernova is the first exciting case with that synergy."
The supernova observed 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 all its nuclear fuel and leaves only a very hot core. (White dwarf temperatures exceed 100,000 degrees Kelvin – nearly 200,000 degrees Fahrenheit.) Unless the star grows larger by stealing pieces of energy and matter from a nearby star, the white dwarf spends the next billions of years cooling before it becomes a lump of black charcoal.
But if the white dwarf and another star are in a binary system, the white dwarf slowly takes mass from the other star to eventually spreads the white dwarf to a supernova.
Type I supernova are important for space science – they help astronomers measure the distance in space and help them calculate how quickly the universe expands (a discovery so important that it won the Nobel Prize in Physics 2011.)
"These are the most known type of supernova – they led to dark energy being discovered in the 1990s, Vallely said. "They are responsible for the existence of so many elements in the universe. But we do not really understand the physics behind them so well. And that is what I really like about combining TESS and ASAS-SN here, that we can build this data and use it to figure out a little more about these supernovae. "
Scientists agree that the companion leads to a white dwarf supernova, but the mechanism of that explosion and the makeup of the companion is less apparent.
This result, Stanek said, provides some evidence that the companion in this type of supernova is probably another white dwarf.
"We see something new in this data and it helps our understanding of Ia-supernova phenomenon," he said. "And we can explain all this in the scenarios we already have – we just need to let the third star in this case be the source of hydrogen. "
ASAS-SN is supported by the Las Cumbres Observatory and is partially funded by Gordon and Betty Moore Foundation, the National Science Foundation, the Mt. astroparticle physics at Ohio State, Chinese Academy of Sciences, South American Center for Astronomy and Villum Foundation in Denmark.