Astronomers have found a “catastrophic” pair of stars with the shortest orbit yet

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Credit: Pixabay/CC0 Public Domain

Almost half of the stars in our galaxy are as isolated as the sun. The other half consists of stars orbiting other stars, in pairs and multiples, with orbits so narrow that some star systems can fit between the Earth and the Moon.


Astronomers at MIT and elsewhere have discovered a stellar binary or pair stars, with a very short orbit, and they seem to orbit each other every 51 minutes. The system appears to be one of a rare class of binaries known as “catastrophic variable,” in which a star similar to our sun tightly orbits a white dwarf — the hot, dense core of a burning star.

The cataclysmic variant occurs when, over billions of years, the two stars get close, causing the white dwarf to start accumulating, or eating material away from the partner star. This process can produce massive, variable flashes of light that astronomers assumed, centuries ago, were the result of an unknown cataclysm.

The newly discovered system, which the team has tagged ZTF J1813 + 4251, is a catastrophic variant with the shortest orbit detected to date. Unlike other systems observed in the past, astronomers detected this cataclysmic variable as the stars dimmed each other several times, allowing the team to accurately measure the properties of each star.

Using these measurements, the researchers ran simulations of what the system likely does today and how it should evolve over the next hundreds of millions of years. They concluded that the stars were currently in transition, and that the sun-like star was spinning and “donating” much of its hydrogen envelope to the voracious white dwarf. The sun-like star will eventually be stripped down to a dense, helium-rich core. In another 70 million years, the stars will migrate closer to each other, with an extremely short orbit of only 18 minutes, before they start expanding and drifting away.

Decades ago, researchers at MIT and elsewhere predicted that such catastrophic variables would have to travel to ultrashort orbits. This is the first time that such a transitional system has been directly observed.

“This is a rare case where we discovered one of these systems during the transition process from hydrogen to accumulating helium,” says Kevin Burdge, Pappalardo’s fellow in the MIT Department of Physics. “People expected that these objects would have to travel to ultrashort orbits, and it has been debated for a long time whether they could get short enough to be emitted. gravitational waves. This discovery relaxes that.”

Burge and colleagues report their discovery in temper nature. The study’s co-authors include collaborators from multiple institutions, including the Harvard and Smithsonian Center for Astrophysics.

sky search

Astronomers discovered the new system within an extensive catalog of stars, observed by the Zwicky Transit Facility (ZTF), a survey that uses a camera attached to a telescope at Palomar Observatory in California to capture high-resolution images of large swaths of sky.

The survey took more than 1,000 images of each star from more than a billion stars in the sky, recording each star’s variable brightness over days, months and years.

Burdge combed the catalog, looking for signs of systems with ultrashort orbits, whose dynamics can be so intense that they must release dramatic bursts of light and emit gravitational waves.

“Gravity waves allow us to study the universe in a completely new way,” says Bridge, who is searching the sky for new sources of gravitational waves.

In this new study, Burdge looked at ZTF data for stars that appeared to flash frequently, with a period of less than an hour — a frequency that typically indicates a system of at least two orbiting objects, where one intersects the other briefly. Block out his light.

Use an algorithm to remove over a billion stars, each of which has been recorded in more than 1,000 images. The algorithm sifted through about a million stars that seemed to blink every hour or so. Among these, Bridget eye looked for signals of particular interest. His research focused on ZTF J1813 + 4251 – a system located about 3,000 light-years from Earth, in the constellation Hercules.

“This thing showed up, where I saw an eclipse that happens every 51 minutes, and I said, ‘OK, that’s definitely a binary,'” Burridge recalls.

dense core

He and his colleagues focused on the system using the WM Keck Observatory in Hawaii and the Gran Telescopio Canarias in Spain. They found that the system was exceptionally “clean,” meaning they could clearly see its light changing with each eclipse. With such clarity, they were able to accurately measure each object’s mass and radius, as well as their own orbital.

They found that the first object was likely a white dwarf, 1/100th the size of the Sun and about half its mass. The second object was a sun-like star towards the end of its life, the size and mass of a tenth of the sun (about the size of Jupiter). The stars also appeared to orbit each other every 51 minutes.

However, there is something that does not add anything.

“This star is like the sun, but the sun can’t fit into an orbit shorter than eight hours – what’s up here?” Bridge says.

He quickly came up with an explanation: Nearly 30 years ago, researchers including MIT professor emeritus Saul Rappaport predicted that ultrashort orbital systems should exist as catastrophic variants. As the white dwarf eats around the sun-like star and turns away from the light hydrogen, the sun-like star must burn up, leaving a core of helium — an element denser than hydrogen and heavy enough to keep the dead star in a tight, ultra-short orbit.

Bridge realized that ZTF J1813 + 4251 was likely a catastrophic variant, in the process of transitioning from a hydrogen-rich to a helium-rich object. The discovery both confirms predictions made by Rappaport and others, and also stands as the shortest orbiting A catastrophic variable discovered so far.

“This is a proprietary system,” says Bridge. “We were doubly lucky to find a system that answers a big open question, one of the most beautifully behaved catastrophic variables known.”


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more information:
Kevin Bridge, a 0.1 solar-mass dense star in a 51-minute orbital period obscuring a binary, temper nature (2022). DOI: 10.1038 / s41586-022-05195-x. www.nature.com/articles/s41586-022-05195-x

the quote: Astronomers have found a pair of ‘catastrophic’ stars with the shortest orbit to date (2022, Oct 5) Retrieved Oct 5, 2022 from https://phys.org/news/2022-10-astronomers-cataclysmic-pair-stars -shortest. programming language

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