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Binary stars are all around us, new map of solar quarters shows

Binary stars are all around us, new map of solar quarters shows

A colorful collage of binary star pairs near Earth, thanks to the Gaia study. Credit: ESA / Gaia / DPAC

The latest star data from the Gaia Space Observatory have, for the first time, enabled astronomers to generate a massive 3-D atlas with widely spaced binary stars within about 3,000 light-years from Earth ̵

1; 1.3 million of them.

The unique atlas, created by Kareem El-Badry, an astrophysics Ph.D. students from the University of California, Berkeley, should be a blessing to those studying binary stars – which make up at least half of all sun-like stars – and white dwarfs, exoplanets and stellar evolution in general. Before Gaia, the last collection of nearby binary stars, compiled using data from the now defunct Hipparcos satellite, included about 200 probable pairs.

“This is just a massive increase in sample size,” El-Badry said. “And it’s an increase in what kind of evolutionary phases we find binaries in. In our sample, we have 17,000 white dwarfs alone. This is a much larger census.”

White dwarfs are the final stages of most stars; the sun is likely to end up as a compact white dwarf in 5 billion years. El-Badry’s atlas includes 1,400 systems consisting of two white dwarfs and 16,000 binary files consisting of a white dwarf and another type of star.

However, the vast majority of the 2.6 million individual stars are still alive. Astronomers refer to them as main sequence stars because they cluster along a line when depicted on a graph showing temperature versus brightness.

With such a large sample size, El-Badry said, it is possible to make population demographics for these star twins and ask questions such as: What is the distribution of mass ratio for the two stars in all these binary systems? How are their separations or eccentricities distributed?

El-Badry plans in the future to focus on the white dwarf binaries because white dwarfs can be assigned an age more accurately than is possible with ordinary stars. Main sequence stars like the sun can look alike for billions or even tens of thousands of billions of years, while white dwarfs change – first, they cool down at a well-defined rate. And since binary pairs are born at the same time, the age of the white dwarf astronomers tells the age of its main sequence twin or about any planets around the stars.

“For a white dwarf, it’s generally easy to tell how old it is – not just how old since it became a white dwarf, but what its overall age is,” he said. “You can also measure their masses because white dwarfs have a well-understood mass radius ratio.”

As an example, El-Badry and colleagues recently used the Gaia data to estimate the age of a Jupiter-sized gas giant discovered by the TESS satellite around a white dwarf K dwarf pair. The exoplanet, TOI-1259Ab, was found to be about 4 billion years old, based on the age of the white dwarf.

Binary stars are all around us, new map of solar quarters shows

When stars are plotted according to their color and brightness, they fall along a line called the main sequence, where they spend most of their lives evolving into red giants and then white dwarfs only at the end of their lives. The previous study of nearby binary stars found several hundred, whereas the latest atlas contains 1.3 million pairs, allowing astronomers to better understand the evolution of binary stars and stars in general. Credit: Kareem El-Badry, UC Berkeley

“In this catalog, there are something like 15 systems like this: star plus planet plus white dwarf,” he said, “and there are a few hundred more that are star plus planet plus another star. They are also potentially interesting because in some cases, the other star will do something dynamic towards the planet. “

The new catalog of nearby binary stars has been accepted for publication in the journal Monthly announcements from the Royal Astronomical Society.

El-Badry also collaborated with Jackie Faherty, a scientist and lecturer at the American Museum of Natural History in New York City, to create a video streaming of all the millions of binary stars around the Earth that represent a good portion of the entire Milky Way. Road Galaxy.

Binary stars

Until Gaia was launched by the European Space Agency in 2013 to accurately measure the distances and motions of millions of nearby stars, the only way to find binary files was to look for stars close together in the sky. This can be cumbersome because stars that look very close to the earth could be hundreds to thousands of light-years apart and simply sit along the same line of the site.

Excluding a chance adjustment requires lots of observation time to confirm that the two candidates are actually at the same distance and moving together. Due to the Earth’s motion around the sun, it appears that nearby stars are changing position in the sky, and that parallax can be used to calculate how far away they are. The movement of the star across the sky, known as proper motion, helps determine its velocity.

Gaia continuously performs this tedious astrometry for all nearby stars in the sky, 24/7, from its orbit at the Earth-Sun Lagrange point. The study of the Space Telescope is most useful for stars within about 3,000 light-years from Earth, but beyond that the parallax is usually too small to measure.

El-Badry only looked for binary stars in Gaia data after the mission’s second release of star measurements in 2018 with the help of colleagues Hans-Walter Rix, director of the Max-Planck Institute for Astronomy in Heidelberg, Germany, and Tyler Heintz, a graduate student at Boston University. They developed computational techniques to identify stars that move together through space and at the same distance from Earth. The technique basically projects the motion of each star over thousands of years based on its proper motion today and pulls out stars that move in the same direction. If they also turn out to be at the same distance based on parallax, they are likely bound to each other, he said.

He and his colleagues focus primarily on wide angles – those separated by a distance of 10 AU (astronomical units) or more – that is, 10 or more times the distance between Earth and the Sun (93 million miles). Stars closer to it typically appear as a point of light and require other spectroscopic techniques to distinguish whether they are true binaries.

A projection into the future of movements of binary star pairs near our sun. Credit: Animation by Jackie Faherty, AMNH, based on data from Kareem El-Badry, UC Berkeley

To get the first crack at Gaia’s latest data, El-Badry emerged at. 3 on the release date of December 3 last year and joined about 100 other astronomers from around the world on Zoom. He quickly ran pre-programmed queries on the data to extract the catalog information he needed to create the 3-D card.

The original queries returned approx. 1.8 million binary candidates from Gaia’s 1.8 billion star catalog, so El-Badry first had to assess the probability that some of the pairs were at the same distance and moving in similar directions at random, not because they are paired. He estimates that nearly 1.3 million couples had at least a 90% chance of getting married, and 1.1 million had a 99% chance.

“About half of all sun-like stars are binary, many of them are too close to distinguish, but we find something along the lines of 25% of all sun-like stars have a binary companion at separations of more than 30 AU, approximately the distance to Pluto, “he said. “The distribution peaks at a separation of 30 or 50 AU.”

Some pairs are separated by as much as one parsec – 260,000 AU or 3.26 light-years – though most are within 1,000 AU apart.

One takeaway, he said, is that the new analysis confirms something hinted at in the 2018 data: Many binary star pairs are very similar in mass.

“One thing we’ve already found is cool – we discovered this with the Gaia DR2, but now we can study it better with this sample – is that binaries like identical twins,” he said. “It’s really weird because most of these are separated by hundreds or thousands of AUs, so they’re so far apart that their masses by conventional star formation theories have to be random. But the data tells a different story: They know something about their escorts. “

The implication, he said, is that they formed much closer together in a process that tended to equalize their masses and then migrate apart, perhaps due to interaction with other nearby stars.

The composition of binary stars also allowed El-Badry to check the reported uncertainties in Gaia’s measurements of star positions, which may help other researchers using the data.

White dwarf atmospheres may contain the powdered crust of their dead planets

More information:
Kareem El-Badry et al., One million Gaia eDR3 binaries: sample selection and validation of Gaia parallax uncertainties, Monthly announcements from the Royal Astronomical Society (2021). DOI: 10.1093 / mnras / stab323

Provided by the University of California – Berkeley

Citation: Binary stars are all around us, new map of solar quarters shows (2021, February 22) retrieved February 23, 2021 from https://phys.org/news/2021-02-binary-stars-solar-neighborhood.html

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