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Binary stars are all around us, a new map of the sunny neighborhood shows

Binary stars are all around us, a new map of the sunny neighborhood shows

Color collage of double pairs of stars near the Earth provided by Gaia̵

7;s study. Credit: ESA / Gaia / DPAC

The latest stellar data from the Gaia Space Observatory for the first time allowed astronomers to generate a massive 3-D atlas of widely divided binary stars within about 3,000 light-years on Earth – 1.3 million of them.

The one-of-a-kind atlas created by Karim El-Badri, a doctoral student in astrophysics at the University of California, Berkeley, should be a boon to those who study 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 latest compilation of nearby binary stars, compiled using data from the now-defunct Hipparcos satellite, included about 200 probable pairs.

“It’s just a huge increase in the sample size,” El-Badri said. “And this is an increase in the type of evolutionary phases in which we find binaries. In our sample, we only have 17,000 white dwarfs. That’s a much larger census.”

White dwarfs are the final stages of most stars; the sun will probably turn out to be a compact white dwarf in 5 billion years. El-Badry’s atlas includes 1,400 systems consisting of two white dwarfs and 16,000 binaries consisting of a white dwarf and another type of star

Most of the 2.6 million individual stars are still in their prime. Astronomers call them stars in the main sequence because they cluster in a line when plotted on a graph showing temperature versus brightness.

With such a large sample size, El-Badri said, it is possible to make a demographics of the population of these stellar twins, asking questions such as: What is the distribution of the mass ratios of the two stars in all these binary systems? How are their sections or eccentricities distributed?

El-Badry plans to focus on white dwarf binaries in the future, as white dwarfs can be age more accurately than ordinary stars. Stars with a basic sequence like the sun can look the same for billions or even tens of billions of years, while white dwarfs change – on the one hand, they cool at a specific rate. And because binary pairs are born at the same time, the age of the white dwarf tells astronomers the age of its twin with a basic sequence or of some planets around the stars.

“For a white dwarf in general, it’s easy to say how old he is – not just how old a white dwarf is, but what his total age is,” he said. “You can also measure their masses because white dwarfs have a well-understood mass-radius relationship.”

As an example, El-Badri and colleagues recently used Gaia data to calculate the age of a gas giant the size of Jupiter, discovered by the TESS satellite around a white dwarf-K pair. This exoplanet, TOI-1259Ab, turned out to be about 4 billion years old, based on the age of the white dwarf.

Binary stars are all around us, a new map of the sunny neighborhood shows

When stars are applied according to their color and brightness, they fall along a line called a basic sequence, where they spend most of their lives evolving into red giants and then white dwarfs only at the end of their lives. A previous study of nearby binary stars found several hundred, while 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

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

The new catalog of nearby binary stars has been accepted for publication in the magazine Monthly notices of the Royal Astronomical Society.

El-Badri also collaborated with Jackie Faherty, a scientist and professor at the American Museum of Natural History in New York, to create a video of all millions of binary stars orbiting the Earth, which is a good part of the entire Milky Way 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 binaries was to search for stars close to each other in the sky. This can be complicated because stars that look very close to Earth can be hundreds to thousands of light-years apart just sitting on the same line on the site.

Excluding random alignment requires a lot 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, nearby stars appear to change position in the sky, and this parallax can be used to calculate how far away they are. The movement of a star in the sky, known as proper motion, helps determine its speed.

Gaia conducts this annoying astrometry continuously for all nearby stars in the sky, 24/7, from its orbit at the Earth-Sun point Lagrange. The study of the space telescope is most useful for stars within about 3,000 light-years from Earth, because in addition, parallax is usually too small to measure.

El-Badry is looking for binary stars in Gaia data for the first time since the second release of stellar measurements in 2018 with the help of colleagues Hans-Walter Ricks, director of the Max-Planck Institute of Astronomy in Heidelberg, Germany, and Tyler Heinz, 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 for thousands of years, based on its proper motion today, and subtracts stars that move in the same direction. If they also find themselves at the same distance based on parallax, they are probably tied to each other, he said.

He and his colleagues focus mainly on large binaries – those separated by 10 AU (astronomical units) or more, ie. 10 or more times the distance between the Earth and the Sun (93 million miles). Stars closer than this usually appear as a single point of light and require other spectroscopic techniques to distinguish whether they are true binaries.

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

To get the first information on Gaia’s latest data, El-Badry appeared at 3 a.m. on the release date, December 3 last year, and joined 100 other astronomers from around the world on Zoom. It quickly executes pre-programmed data queries to retrieve the information from the catalog it needs to create the 3D map.

Initial inquiries returned about 1.8 million binary candidates from Gaia’s 1.8 billion-star catalog, so El-Badry first had to assess the likelihood that some of the pairs were equidistant and moving in similar directions quite by accident. because they are paired. He estimates that nearly 1.3 million couples had at least a 90% chance of being engaged, and 1.1 million had a 99% chance.

“About half of all sun-like stars are binary files, many too close to be different, but we find that about 25% of all sun-like stars have a binary satellite at sections above 30 AU, approximately the distance to Pluto, “he said.” The distribution peaks are at a division of 30 or 50 AU. “

Some pairs are separated by a parsec – 260,000 AU or 3.26 light-years – although most are within 1,000 AU of each other.

According to him, one of the options is that the new analysis confirms something hinted at in the data for 2018: Many double pairs of stars are very similar in mass.

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

The implication, he said, is that they came much closer together in a process that tended to flatten their masses and then migrated apart, perhaps due to interactions with other nearby stars.

The compilation of binary stars also allowed El-Badri to verify the reported uncertainty in Gaia’s measurements of stellar positions, which could help other researchers using the data.

The atmospheres of white dwarfs may contain the pulverized crusts of their dead planets.

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

Provided by the University of California, Berkeley

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

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