A newly compiled 3D map has revealed more than 1 million binary star pairs located within 3,000 light-years of Earth, emphasizing the ubiquity of these celestial objects.
Remember that sublime moment in Star Wars when an introspective Luke Skywalker watches a double sunset on Tatooine? To our eyes, these are some exotic things, but binary star systems are actually quite common, representing at least half of all Sunny stars in the Milky Way. That said, a solid portion of this includes ‘wide binaries’, whose distances between stellar companions exceed 10 AU, or 10 times the average distance from Earth to the Sun (this is also a comparable distance between Earth and Saturn ).
New research published in the monthly notices of the Royal Astronomical Society provides a count of these wide binaries, at least up to within 3000 light-years of Earth. The new paper, led by astrophysicist Kareem El-Badry, a PhD student at the University of California, Berkeley, describes the relative locations of 1.3 million binary pairs spread across much of the Milky Way, which measuring more than 100,000 light-years. diameter. Jackie Faherty of the American Museum of Natural History in New York worked with El-Badry to produce a beautiful video feed of the newly mapped binary pairs.
To compile the new 3D atlas, El-Badry used data collected by ESA’s Gaia space telescope, which was in orbit at the Earth-Sun Lagrange point – which lovely place between two large objects that allow spacecraft like Gaia to stay seated – since 2013.
Finding binary stars that are close to each other is a relatively simple process (you need a spectrometer), but finding a wide binary is completely different. This is where Gaia comes in, with its ability to measure the position and real motion of stars in the environment, which it does for millions of objects. That said, it cannot follow stars beyond 3,000 light-years away, hence the limited scope of the new census.
Broad binaries are “easy to study with the Gaia spacecraft, because at wide separations the two stars can be spatially resolved as two different points of light in the sky,” El-Badry explained in an email. “On closer separation, binaries are not resolved, so other methods (such as spectroscopy) are needed to detect them.”
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El-Badry, along with colleagues from the Max Planck Institute for Astronomy and Boston University, developed a computational technique to indicate pairs of stars moving through space together and at the same distance from Earth. For this analysis, El-Badry used data from the December 3, 2020 Gaia release, which included nearly 2 billion stars.
It is important that this technique, like some stars, can only lead to false positives. appear to have companions, with objects moving in space with each other in concert, but by total coincidence. (The authors call it ‘random alignment’.) El-Badry estimates that 1.3 million pairs identified in the study have a 90% chance of being true binary stars. This is a great deal of uncertainty and an area where this research can be improved.
The new catalog also contains a significant number of white dwarfs, the warm, dense remnants of former stars. About 1,400 systems listed in the catalog consist of two white dwarfs, while 16,000 systems consist of one 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 his colleagues also found that about 25% of all solar stars have companions that are further away than 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 a few pairs separated by an entire parsec, or 3.26 light-years. However, this was extraordinary because most binary stars were found to be located within 1000 AU of each other. At such distances, it is reasonable to wonder whether these pairs can even be considered companions, but El-Badry said double stars exist over an enormous variety of physical separation.
“The nearest binaries have separations smaller than the Earth-Moon distance, and orbital periods of only a few minutes,” he explained. ‘The widest have separations up to a few light years, and orbital periods of more than 100 million years. This means that at the widest separations the two stars orbit the Milky Way about once per orbit, and that they have only completed a few dozen orbits since they formed. The acceleration of gravity at such wide separations is, of course, extremely weak, but not entirely negligible. ”
Another interesting observation is that many binary pairs have a similar mass. This is strange, especially given the distances between some of these objects.
‘One surprising result from our study is that even at separations of thousands of AU there is a strong excess of’ identical twin ‘binaries in which the two stars have almost the same mass. [to] within a few percent, ”El-Badry said. “This was not expected, as conventional star formation theory predicts that the two stars at these distances form basically independently, so that their masses should not be strongly correlated.”
This observation may speak to star formation theories, with binary pairs forming together in the same star nursery, and then slowly drifting apart over time. As El-Badry noted, “how this population will be formed will require more work, both in terms of theory and observations.”