A recently compiled 3D map revealed more than 1 million pairs of binary stars located 3,000 light-years from Earth, highlighting the ubiquity of these celestial objects.
Remember that sublime time in the Star Wars when an introspective Luke Skywalker watches a double sunset on Tatooine? To our eyes, these are seriously exotic things, but binary star systems are actually quite common, accounting for at least half of all Milky Way-like stars. That being said, a significant portion of these include “wide binaries”, in which the distances between stellar companions exceed 10 AU, or 10 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 Notifications of the Royal Astronomical Society provides a census of these wide tracks, at least those at a distance of 3,000 light-years from Earth. The new work, led by astrophysicist Kareem El-Badry, a doctoral student at the University of California, Berkeley, recounts the relative locations of 1.3 million binary pairs spread over a good chunk of the Milky Way, which is 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 amazing flight video 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 – that sweet spot between two large objects that allow spacecraft such as Gaia to remain seated – since 2013.
Finding binary stars parked close to each other is a relatively simple process (you need a spectrometer), but finding wide binaries is something else entirely. This is where Gaia comes in, with her ability to measure the correct position and motion of nearby stars, which is done for millions of objects. That being said, it can’t really track stars more than 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 resolved spatially as two distinct points of light in the sky,” El-Badry explained in an e-mail. “At tighter separations, binaries are unresolved, so other methods (such as spectroscopy) are needed to detect them.”
G / O Media may receive a commission
El-Badry, along with colleagues at the Max Planck Institute for Astronomy and Boston University, developed a computational technique to identify pairs of stars that move together through space and at the same distance from Earth. For this analysis, El-Badry used data from the December 3, 2020 version of Gaia, which included nearly 2 billion stars.
Importantly, this technique can lead to positive fakes, like just some stars appear to have companions, with objects that move through space, concerted with each other, 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 where this research could be improved.
The new catalog also includes a considerable number of white dwarfs, the hot and dense remains of former stars. Approximately 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 the stars in the catalog are main sequential stars, which are still in the main phase of their existence.
El-Badry and his colleagues also found that about 25% of all Sun-like stars have companions at a distance of more than 30 AU, which is about 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, these were abnormal values, as it was found that most binary stars are located at a distance of 1,000 AU from each other. At such distances, it is fair to ask whether these pairs can even be considered companions, but El-Badry said that double stars exist in a huge range of physical separation.
“The nearest tracks 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 in orbit around the Milky Way and have completed only a few dozen orbits since they formed. Of course, the gravitational acceleration at such wide separations is extremely weak, but not completely negligible. ”
Another interesting observation is that many binary pairs have a similar mass. This is strange, especially given the distances involved between some of these objects.
“A surprising result from 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 an almost equal mass. [to] in a few percent, “El-Badry said.” This was not to be expected, because the conventional theory of star formation predicts that at these distances, the two stars form practically independently, so their masses should not be strongly correlated. . ”
This observation could talk about star-forming theories, with binary pairs forming together in the same star nursery and then slowly moving away in time. As El-Badry pointed out, “the way this population was formed will require more work, both in terms of theory and observations.”