Supernova unveils rare pair of stars in the Milky Wayas it made more of a fizz and less of a bang. The explosion, called a "ultra-stripped" supernova, was so weak that it led scientists to find the two stars 11,000 light-years from Earth.
It's the first confirmed discovery of a system of stars that will one day create a kilonova, which happens when two neutron stars crash into each other and explode, sending gold and other heavy elements into space. It is thought that there are only about 10 other pairs of stars like this in the Milky Way galaxy. It took a long time to find out about it.
In 2016, NASA's Neil Gehrels Swift Observatory saw a big flash of X-ray light coming from the same part of the sky as a hot, bright Be-type star. Astronomers wanted to find out if the two could be linked, so they used the 1.5-meter telescope at the Cerro Tololo Inter-American Observatory in northern Chile to gather data.
Dr. Noel D. Richardson, an assistant professor of physics and astronomy at Embry-Riddle Aeronautical University, was interested in using this information to learn more about the star. In 2019, Clarissa Pavao, an undergraduate student at the university, went up to Richardson while she was in his astronomy class and asked if he had any projects she could work on to learn more about astronomy research.
He gave her the data from the telescope, and while the pandemic was going on, Pavao learned how to clean up the data from the telescope in Chile to make it less distorted.
The telescope looks at a star and it takes in all the light so that you can see the elements that make up this star - but Be stars tend to have disks of matter around them. It’s hard to see directly through all that stuff.- Clarissa Pavao, an undergraduate student at Embry-Riddle Aeronautical University
She sent Richardson her first results, which looked a bit like a scatterplot. Richardson saw that she had found an orbit for the two-star system. Observations that came afterward helped them confirm the orbit of the two-star system CPD-29 2176.
But they weren't expecting that orbit. Most of the time, two stars that are close to each other orbit around each other in an oval shape. In CPD-29 2176, one star goes around the other in a circle about once every 60 days.
The two stars, one bigger than the other, were going around each other very close to each other. Over time, Richardson said, the bigger star started to lose hydrogen, which caused the material to fall onto the smaller star and make it grow from 8 or 9 times the mass of our sun to 18 or 19 times the mass of our sun. To give you an idea, the mass of our sun is 333,000 times that of Earth.
Several stars in the milky way
As the secondary star grew, the main star got smaller and smaller. When it ran out of fuel, there wasn't enough left to make a big, powerful supernova to send its remaining matter into space. Instead, it was like setting off a bad firework.
The star was so depleted that the explosion didn’t even have enough energy to kick (its) orbit into the more typical elliptical shape seen in similar binaries.- Dr. Noel D. Richardson, an assistant professor of physics and astronomy at Embry-Riddle Aeronautical University
After the ultra-stripped supernova, a dense object called a neutron star was all that was left. This neutron star now circles the fast-rotating massive star. The pair of stars will stay in the same place for another 5-7 million years. Since the Be star got both mass and angular momentum, it sends out a disk of gas to keep itself in balance and make sure it doesn't tear itself apart.
At some point, the second star will run out of fuel, expand, and send out material, just like the first star did. But it would be hard to put all of that stuff on the neutron star, so the star system will send it out into space. The second star will probably have a supernova like the first one, which won't be very exciting and turn into a neutron star.
Over time, which is probably a couple of billion years, the two neutron stars will merge and then explode in a kilonova, sending heavy elements like gold out into the universe.
“Those heavy elements allow us to live the way that we do. For example, most gold was created by stars similar to the supernova relic or neutron star in the binary system that we studied. Astronomy deepens our understanding of the world and our place in it,” Richardson said.
Pavao said, “When we look at these objects, we’re looking backward through time.” “We get to know more about the origins of the universe, which will tell us where our solar system is headed. As humans, we started out with the same elements as these stars." The results of their study were published in the journal Nature on Wednesday.
Richardson and Pavao also worked with a physicist at the University of Auckland in New Zealand named Jan J. Eldridge. Eldridge is an expert on binary star systems and how they change over time. Eldridge looked at thousands of models of binary stars and decided that there are probably only 10 more like the one in their study in the whole Milky Way galaxy.
Next, the researchers want to learn more about the Be star itself. They hope to use the Hubble Space Telescope to make more observations. Pavao also wants to get her degree and use the new skills she has learned to keep working on space physics research.
Pavao said, “I never thought I would be working on the evolutionary history of binary star systems and supernovas. It’s been an amazing project.”