Light Curves of LiGO/Virgo GW170817/SSS17a and Comparison to kilonova Models

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The 2016 Swift X-ray Flash from the Be Star CPD-29 2176: An Extrasolar, Rapidly-Evolving Nova?

Heavy elements from the universe will be released when the two Neutron stars come together over a couple billion years.

In 2016, NASA’s Neil Gehrels Swift Observatory detected a large flash of X-ray light, which originated from the same region in the sky where a hot, bright Be-type star was located.

Astronomers were curious if the two could potentially be linked, so data was captured using the Cerro Tololo Inter-American Observatory’s 1.5-meter telescope in northern Chile.

One of those interested in using this data to learn more about the star was Dr. Noel D. Richardson, now an assistant professor of physics and astronomy at Embry-Riddle Aeronautical University.

Clarissa Pavao, an undergraduate student at the University, asked Richardson if he had any astronomy research projects she could work on to gain experience with astronomy research. Pavao learned how to clean up the telescope data after he shared it with her, as he shared the telescope data with her.

“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,” Pavao said. “It’s hard to see directly through all that stuff.”

She sent her initial results — which resembled something like a scatterplot — to Richardson, who recognized that she had pinned down an orbit for the double-star system. Follow-up observations helped them verify the orbit of the binary star system, named CPD-29 2176.

The two stars were in a close circle around each other. Over time, the larger star had begun to shed its hydrogen, releasing material onto the smaller star, which grow from 8 or 9 times the mass of our sun to 18 or 19 times the mass of our sun, Richardson said. Our sun has a mass of 333,000 times that of Earth.

While the main star was small and the secondary star was bigger, there weren’t enough of its remaining material to generate a large, energetic nova to release into space.

“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,” Richardson said.

What remained after the ultra-stripped supernova was a dense remnant known as a neutron star, which now orbits the rapidly rotating massive star. The stellar pair will remain in a stable configuration for about 5 to 7 million years. To maintain balance it releases gas to make sure it doesn’t rip itself apart, because both mass and force were transferred to the Be star.

Eventually, the secondary star will also burn through its fuel, expand and release material like the first one did. The star system will release the material through space since it can’t easily be piled up onto the neutron star. The secondary star will likely experience a similar lackluster supernova and turn into a neutron star.

Source: https://www.cnn.com/2023/02/01/world/supernova-rare-star-pair-scn/index.html

Stellar Genealogy: How Many Stars Live In the Milky Way? A Case Study of Two Relics and One Nearby Neutron Star

“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. Richardson said that Astronomy deepens our understanding of the world.

Pavao says that we look at the objects 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.”

Richardson and Pavao also worked with physicist Jan J. Eldridge at the University of Auckland in New Zealand, an expert on binary star systems and their evolution. Eldridge reviewed thousands of binary star models and estimated there are likely only 10 in the entirety of the Milky Way galaxy similar to the one in their study.

Researchers want to learn more about the Be star, and hope to use the Hubble Space Telescope to do so. Pavao wants to graduate and continue her space physics research using the new skills she has acquired.

Forget archaeologists and their lost civilizations, or paleontologists with their fossils—astrophysicist Heloise Stevance studies the past on an entirely different scale. Astronomers can catch a glimpse of an unusual signal in the sky and then use Stevance to back up their clock by billions of years. Working at the University of Auckland in New Zealand, she traces the past lives of dead and dying stars, a process she calls stellar genealogy. “There’s a lot of drama in the lives of stars,” she says.

Researchers don’t know how common these mergers are, and they can’t tell whether they are responsible for creating all the heavy elements in the universe, or just a fraction. If astrophysicists could observe more mergers, they could answer even deeper questions, such as how old the universe is. This is where stellar genealogy can help.

The work also describes interactions between the two stars before they burned out their fuel to become neutron stars. They started tens of millions of kilometers apart, which sounds far but is actually well under the distance between Earth and the Sun. Each star was surrounded by gas. Stevance and her team’s models determined that over the stars’ lifetimes, one star’s envelope engulfed the other—that is, their outer gases merged to become a single shared envelope—at least twice.

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