July 29, 07:10

Astronomers discover candidate for planetary-mass companion around star Tabby

Astronomers have hypothesized the existence of a large moon orbiting the well-known star Tabby, which could be either a giant exoplanet or a brown dwarf. This suspicion was supported by an event resembling a transit. If this discovery is confirmed, it may help explain the irregular and unusual dips in the star's brightness, caused by swarms of small objects moving towards the star under the gravitational influence of this planetary-mass companion. The full text of the study is available on the arXiv.org platform.

For a long time, KIC 8462852 was considered a typical main-sequence star, classified as F3V and located 1470 light-years from the Sun. However, in 2015, astronomers recorded unusual, prolonged, and uneven changes in the star's brightness that had no obvious explanation. Since then, Tabby's star, named after the leader of the scientific group that first noted this variability, has remained one of the unresolved problems in astrophysics.

Possible Explanations for the Dimming

Many hypotheses were proposed to explain the multiple, asymmetric, and irregular drops in the star's brightness: these could be transits of exocomets, clusters of Trojan asteroids, rings of debris formed by the tidal forces of a large planetesimal or protoplanet, the presence of a stellar companion, a compact object, or a brown dwarf, manifestations of stellar activity (such as spots or plasma ejections), or even hypothetical astroengineering structures like a Dyson sphere. Although none of these versions has been definitively proven, theories about the transits of families of small bodies, rings, and associated objects seemed the most promising.

Data Analysis and Transit Detection

A team of astronomers led by Christine Madourga-Favier from the University of Warwick focused on studying the applicability of transit models to the behavior of Tabby's star. To do this, they analyzed photometric observation data collected by the TESS space telescope, as well as radial velocity variation data obtained using the HARPS, SOPHIE, and HERMES spectrographs. The study covered the period from 2015 to 2025, including the use of archival data from the Kepler telescope and ground-based observatories.

TESS data revealed an interesting symmetric dip in brightness of 1.1 percent, lasting about 21 hours and occurring on September 3, 2019. This phenomenon is best described as the transit of a large body across the star's disk, whereas other options, such as asteroid group transits, exocomets, dust clouds, or stellar activity, do not fit. Similar events were not found in Kepler or ground telescope records, nor could they have been caused by a dim red dwarf orbiting Tabby's star at a wide orbit (projected distance of about 885 astronomical units).

Characteristics of the Proposed Companion

The study of radial velocity variations allowed researchers to focus on the model of a transit candidate. This object is estimated to have a mass of about 9.4 Jupiter masses (with an upper limit of 28 Jupiter masses) and a radius of 1.7 Jupiter radii, placing it in the transition zone between gas giants and brown dwarfs. Furthermore, the calculated bulk density (2.2 g/cm³) and equilibrium temperature (268 K) are more consistent with the model of a large exoplanet than a substellar object. The candidate's orbit must be at a distance of approximately 0.005 arcseconds from the star, corresponding to a slightly eccentric orbit (eccentricity 0.09) with a semi-major axis of 2.35 astronomical units and a period of at least 1030 days.

Conclusions and Future Research

Although only one recorded transit and significant scatter in the radial velocity data do not provide sufficient confidence to confirm the presence of a planetary-mass companion, the statistical significance of the calculated physical parameters is only 2.3 sigma. Nevertheless, the presence of such a body is consistent with the distribution of properties of giant exoplanets around stars and may explain the infall of streams of exocomets or fragments of planetesimals causing irregular dips in brightness through gravitational perturbations. The presence of dust around this companion is also not ruled out. Scientists believe that confirming a planetary-nature moon is possible using astrometric data from the Gaia fourth catalog, and a more precise determination of its characteristics will require data from the Hubble and James Webb space telescopes.

Tabby's star is one of the first examples of observing exotic dimmings; subsequently, scientists were able to observe transits of exocomets, dust rings, and brown dwarfs surrounded by them around their stars. It is also worth noting that ground-based telescopes VLT and Gemini-North recorded a decrease in wind speeds on seven ultra-hot Jupiters as the equilibrium temperature increased, which, according to estimates, may be explained by the braking effect of a planetary magnetic field whose strength is comparable to the fields of Jupiter and Saturn. This article was published in the journal Nature Astronomy.

nplus1.ruJuly 28, 15:00

Astronomers re-discover Betelgeuse companion star, requiring further confirmation

Scientists have once again been able to directly detect the companion star of the red supergiant Betelgeuse. The properties of this new object match the model of a young star located near the red supergiant. However, final confirmation of its existence is only possible one year after calculating the companion's orbit.

Scientific Publications and Information Sources

The details of this work will be presented in the scientific journal Astronomy & Astrophysics, and a summary of the research is available on the European Southern Observatory website.

Characteristics of Red Supergiants

Red supergiants represent the final evolutionary stage of massive stars whose initial mass was between 8 and 30–35 solar masses. These stars are precursors to Type II P or Type II L supernova explosions. It is assumed that most massive stars form in systems with two or more luminous bodies, but among red supergiants, such binary systems occur significantly less often—only in 20–40 percent of cases. Existing theories explaining this phenomenon through mass transfer or stellar merger before the red supergiant stage require verification with extensive observational data.

History of Betelgeuse Study

Betelgeuse is the closest representative of the red supergiant class, located in the constellation Orion at a distance of 597–689 light-years. The hypothesis of having one or more companion stars was first proposed at the end of the last century but remained unconfirmed for a long time. Previously, astrometry data and measurements of radial velocity variations indicated the system's binary nature, which helped explain some aspects of periodic brightness changes. However, attempts to find this star using deep optical and X-ray observations with the Hubble and Chandra telescopes were unsuccessful, leading to the suggestion that the companion might be a low-mass young object. This theory initially received preliminary evidence from direct observations, and later indirect evidence related to the wave generated by the companion in the surrounding gas. Despite this, scientists lacked sufficient data for definitive confirmation.

New Direct Detection of Companion

A team of astronomers led by Miguel Montarjes from the Paris Observatory reported the re-detection of Betelgeuse's companion. The discovery was made using the SPHERE instrument and the ZIMPOL polarimeter installed on the ground-based VLT telescope complex in Chile. Observations were conducted from December 3 to 6, 2024, utilizing an adaptive optics system to correct for atmospheric distortions.

Observation Results and Candidate Characteristics

Using the NHa filter (narrow H-alpha line centered at 656.34 nanometers), no sources were detected. However, when observing with the CntHa filter (continuum near H-alpha Hα, centered at 644.9 nanometers) near Betelgeuse, a source of radiation appeared that is excluded as a background object or foreground star. The spatial location of this source matches previous direct observation results, and the statistical significance of the discovery reaches 6.1 sigma. The object is currently considered a candidate because additional observation is required in one year, when the star will occupy a different position in its orbit, allowing for precise calculation of its parameters. At the time of measurement, the candidate was located at a distance of about 8.8 astronomical units from Betelgeuse. The presumed orbital period of the object is at least 5.9 years, and it could be a young main-sequence star with a mass ranging from 2.6 to 3.1 solar masses. Difficulties in determining the companion's parameters are exacerbated by uncertainties in the mass of Betelgeuse itself and its distance from Earth. Nevertheless, researchers believe that the presence of the companion helps adequately explain the long-period variability of the main star's brightness, which is about 2200 days. Previously, Betelgeuse experienced a sharp drop in brightness, which was initially linked to the beginning of the star's death, but it was later found to be a plasma ejection, making the idea of the star's imminent demise less likely.