A recently compiled 3D map has revealed more than a million pairs of binary stars located about 3,000 light-years from Earth, highlighting the ubiquity of these celestial objects.
Remember the sublime moment inside Star Wars when an introspective Luke Skywalker contemplates a double sunset on Tatooine? To our eyes, this is a seriously exotic thing, but binary star systems are actually quite common, as they represent at least half of all Sun-like stars in the Milky Way. That said, a significant portion of these include “wide binaries,” in which the distances between stellar companions exceed 10 AU, or ten times the average distance from Earth to the Sun (it is also a comparable distance between Earth). and Saturn).
New research published in the Monthly Notices of the Royal Astronomical Society provides a census of these broad binaries, at least about 3,000 light-years from Earth. The new paper, led by astrophysicist Kareem El-Badry, a doctoral student at the University of California, Berkeley, narrates the relative locations of 1.3 million binary pairs spread over a good chunk of the Milky Way, which measures more than 100,000 light-years in diameter. Jackie Faherty, of the American Museum of Natural History in New York, worked with El-Badry to produce an impressive video on the newly mapped binary pairs.
To compile the new 3D atlas, El-Badry used data collected by ESA’s Gaia space telescope, which has been in orbit at the Lagrange Earth-Sun point, which sweet spot between two large objects that allow to maintain spaceships like Gaia, since 2013.
Finding binary stars parked nearby is a relatively simple process (a spectrometer is needed), but finding wide binaries is another matter. That’s where Gaia comes in, with its ability to measure the proper position and motion of nearby stars, made for millions of objects. That said, it can’t actually track stars more than 3,000 light-years away, hence the limited scope of the new census.
The broad binaries are “easy to study with the Gaia spacecraft, because at great distances the two stars can be resolved spatially as two different points of light in the sky,” El-Badry explained in an email. “At closer separations, the binaries are unresolved, so other methods (such as spectroscopy) are needed to detect them.”
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El-Badry, along with colleagues at the Max Planck Institute for Astronomy and Boston University, developed a computational technique to identify pairs of stars moving together through space and at the same distance. of the Earth. For this analysis, El-Badry used data from the December 3, 2020 Gaia launch, which included nearly 2 billion stars.
It is important to note that this technique can lead to false positives, as only a few stars appear to have companions, with objects that move by the space of concerted way, but by total coincidence. (The authors call these “random alignments”). El-Badry estimates that 1.3 million pairs identified in the study have a 90% chance of being true binary stars. This is a high degree of uncertainty and an area in which this research could be improved.
The new catalog also includes a considerable number of white dwarfs, the dense, hot remains of old stars. About 1,400 systems listed in the catalog consist of two white dwarfs, while 16,000 systems consist of a white dwarf and another type of star. The vast majority of stars in the catalog are main sequence stars, which are still in the main phase of their existence.
El-Badry and colleagues also found that about 25% of all Sun-like stars have companies located farther from 30 AU, which is approximately the distance between Earth and Pluto. Distances between 30 and 50 AU are common, but the team also managed to document binaries at extreme distances, including some pairs separated by an entire parsec, or 3.26 light-years. However, they were atypical values, as most binary stars were found to be less than 1,000 AU apart. At these distances, it’s fair to wonder if these couples can even be considered companions, but El-Badry said double stars exist in a huge range of physical separations.
“The nearest binaries have smaller separations than the Earth-Moon distance and orbital periods of only a few minutes,” he explained. “The largest have separations of up to a few light years and orbital periods exceeding 100 million years. This means that at the widest separations, the two stars orbit each other only once per orbit around the Milky Way and have only completed a few dozen orbits since they formed. Of course, the gravitational acceleration at such wide separations is extremely weak, but not entirely insignificant.
Another interesting observation is that many binary pairs have a similar mass. This is strange, especially considering the distances involved between some of these objects.
“A striking result of our study is that, even at thousands of AU separations, there is a strong excess of‘ identical twin ’binaries in which the two stars have almost equal mass. [to] by a few percent, “El-Badry said.” This was not expected, as conventional star-forming theory predicts that at these distances, the two stars form basically independently, so that the stars their masses should not be strongly correlated. “
This observation could speak of theories of star formation, with binary pairs forming together in the same star nursery and then deviating slowly over time. As El-Badry noted, “how this population will be formed will require more work, both in theoretical terms and in terms of observations.”