Track the interstellar object & nbsp; Oumuamua to his home

The discovery of the interstellar object called Oumuamua in October 2017 was a first: for the first time, astronomers were able to visit an interstellar object visiting our solar system. Unfortunately, the visitor was caught just as he was leaving, but astronomers were still able to use ground telescopes and space telescopes to measure the movement of the object.

At present, a group of astronomers led by Coryn Bailer-Jones has managed to trace the movement of Oumuamua and identify four candidate stars whose interstellar object could have come from. Previous studies had attempted similar reconstructions of the origin of Oumuamua, but had not proposed plausible candidates.

A crucial new ingredient

These previous studies lacked an essential ingredient: in June 2018, a group led by ESA astronomer, Marco Micheli, had shown that "the orbit of Oumuamua in the solar system does not exist. Is not that of an object in free fall, that is to say the influence of gravity. Instead, there was an extra acceleration when the object was close to the sun. The probable explanation is that "Oumuamua has a certain similarity to a comet – with ice sufficiently heated by sunlight, it produces a gas which in turn accelerates the source object like an extremely weak rocket motor. . Although weak (degassing was not visible on images as with comets near the Sun), it is too large to be ignored when tracking the orbit.

The new study by Bailer-Jones and his colleagues takes into account how the orbit of Oumuamua changed as the object passed near the Sun, giving astronomers an accurate estimate of the original direction of the object, as well as the speed at which entered our solar system.

Harnessing Gaia's data treasures

This could take care of the way "Oumuamua entered the solar system, but what about the stars encountered on the way, and their combined gravity that will have influenced the trajectory of the object? For this part of the reconstruction, Bailer-Jones used a treasure trove of data that Gaia's ESA mission released last April, Gaia's Data Release 2 (DR2). As the head of one of the groups responsible for preparing Gaia data for use by the scientific community, Bailer-Jones is very familiar with this dataset. In particular, DR2 includes accurate position information, sky motion, and parallax (as a measure of distance) for 1.3 billion stars. For seven million of them, there is also information on the radial velocity of the star, that is to say its movement directly from or to us. Using the astronomical Simbad database, astronomers have included 220,000 additional stars in their study, for which radial velocity is available only from the Simbad database.

Then, the astronomers looked at an approximate trajectory: a simplified scenario in which both Oumuamua and all the stars move along straight lines, at constant speed. From this scenario, they selected around 4500 stars who were promising candidates for a closer encounter with 'Oumuamua'. Then came the next step: Trace the past movements for these candidates and for 'Oumuamua using a smoothed version of the gravitational influence of all matter in our original galaxy (the' galactic potential smoothed ").

Search for candidate houses

Various studies had already suggested that "Oumuamua was ejected from the planetary system of its original star during the formation phase of the planet, while many small objects ('planetesimals') were flying around the giant planets of the planet. system. The original star of the object will probably have two key properties: Finding the orbit of Oumuamua will take us back directly to the original star, or the less very close to it. In addition, the relative velocity of Oumuamua and its original star will likely be relatively slow – objects are not usually ejected from their home systems at high speeds.

Bailer-Jones and his colleagues found four stars that are possible candidates for the birthplace of Oumuamua. All four are dwarf stars. The one who came closest to Oumuamua, at least a million years ago, is the reddish dwarf star HIP 3757. He approached at about 1.96 light years. Given the unexplained uncertainties in this reconstruction, it is close enough for Oumuamua to come from its planetary system (if the star has one). However, the relatively high relative speed (about 25 km / s) makes it less likely that it is the home of Oumuamua.

The next candidate, HD 292249, is similar to our Sun, it was a little less close to the object's trajectory 3.8 million years ago, but with a relative speed of less than 10 km / s. The two additional candidates met respectively with Oumuamua 1.1 and 6.3 million years, at intermediate speeds and distances. These stars have already been cataloged by other surveys, but little is known about them.

Other directions

Although these four candidates are plausible, the smoking gun is still missing. In order to eject "Oumuamua at the observed speeds, the host system should have had a suitable giant planet capable of launching Oumuamua into the depths of space. Until now, no planet of this type has been detected around these stars, but as none of the stars has been closely examined for planets, this could well change in the past. ;to come up.

The study is also limited by the limited number of radial velocities included in the second version of Gaia. The third version of Gaia, scheduled for 2021, should provide such data for a sample of stars ten times larger, which could lead to the identification of additional candidates. The search for the house of Oumuamua continues. The study presented here presents interesting candidates, but we have not yet completely followed our interstellar visitor.

The work described here is accepted for publication in the Astrophysical Journal like Bailer-Jones et al. 2018, "Plausible origin stars of the interstellar object" Oumuamua found in GaiaDR2. "

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More information:
Plausible home stars of the interstellar object – Oumuamua found in Gaia DR2, arXiv: 1809.09009 [astro-ph.EP] arxiv.org/abs/1809.09009