Two stars collide in a triple system. Polish astronomers explain the eruption of V838 Monocerotis

In 2002, a star known as V838 Monocerotis (abbreviated: V838 Mon) exploded. This object quickly became an astronomical sensation. Its brightness increased a thousand times in a few weeks, and the so-called light echo effect (the result of light from the scattering of the flash on interstellar dust grains) was also observed. Images of this effect taken by the Hubble Space Telescope are one of the icons of modern astrophotography. At its peak, V838 was one of the brightest stars in the entire Local Group of galaxies to which the Milky Way belongs.

For several years, there has been controversy over the interpretation of this cosmic catastrophe, because its course did not coincide with previously known cosmic explosions. Professor Romuald Tylenda of the Toruń Branch of the Astronomical Center Nicholas Copernicus of the Polish Academy of Sciences (CAMK PAN), together with colleagues, has proposed an explanation for the occurrence of a collision and fusion (merging into a single body) between two stars. Currently, this hypothesis is widely accepted, and organisms of this type are called new red.

Thanks to the case of V838 Monocerotis and similar objects, we know that regular star mergers do occur in our own and other galaxies, that is, in the universe in general. Professor Thailand explained that this happens much more often than mergers of black holes or neutron stars.

Currently, a team of scientists led by Dr. Tomasz Kamiński (CAMK PAN) has analyzed the state of the V838 explosion site after several years. ALMA’s large network of radio telescopes operating on the Chajnantor Plateau in Chile operated by the European Southern Observatory (ESO) was used for this.

Maps obtained with the ALMA interferometer show two stars surrounded by dust. One is a remnant of the collision, and the other is a distant companion whose existence has long been known, but its exact location is unknown. According to ALMA notes, the companion is 250 AU of remnant V838 Mon (250 times more Earth than the Sun).

This means that the two stars have already collided in a triple system. According to the results of astronomers, the components of the inner binary system, the mass of which are 8.0 and 0.4 times the mass of the Sun, were involved in the collision. On the other hand, the distant companion has a mass of 8.0 solar masses and is a hot star.

Data from the ALMA telescope also shows the distribution of molecular gas diffuse during the 2002 eruption. Details can be seen thanks to emissions from carbon monoxide (CO), silicon oxide (SiO), sulfur oxide (SO), sulfur dioxide (SO2) and aluminum hydroxide (AlOH) particles. . The material ejected from the collision of stars is traveling at about 200 kilometers per second (72,000 kilometers per hour) or more. It is known from previous observations that some of these reached the comrade’s hot ocean as early as 2005. This material is so dust-rich that it completely blocks the visible light emitted by the comrade, so its observations have not been optically possible for 14 years. Fortunately, ALMA can “see” the stars even through thick clouds of dust, and even – ironically – thanks to the presence of dust you can now see this star on ALMA maps.

In 2019, previously ejected material had already traveled far beyond its companion’s orbit and formed a spherical symmetric nebula around V838 Mon. However, if you take a closer look at the particles covered by ALMA’s observations, you can see that some of them are only in the vicinity of the companion, and some disappear there. This is the effect of a change in the chemical composition of the gas, mainly due to shock waves generated by the interaction of the star’s gravity with the matter flowing around it. This effect is known from astrochemical research, but it has never been directly observed.

How is the new red different from other types of cosmic explosions? As Dr. Tomas Kaminsky explains, the energy of the new red explosion, that is, the energy associated with the great brightness of the object and the ejection of matter, comes mainly from the gravitational energy of the star system. This new red color, or more generally, distinguishes fusion phenomena from many other types of stellar explosions, such as classical or new supernovae, in which the energy of the explosion comes mainly from thermonuclear reactions, which in turn require very high temperatures. The new red varieties do not require high temperatures and this is one reason why they are so rich in dust and particles.

Just two decades ago, it seemed impossible to notice the collision of stars. Today we know about a dozen such objects, whether in our own or neighboring galaxies, we not only study red nova stellar collisions, but thanks to the use of millimeter interferometry techniques we can see details in objects shortly after the catastrophic action of the star. Cannibalism.

“We expect to see more of these objects with a new generation of observatories such as Vera C. Rubin,” said Professor Tylenda. Objects like V838 Mon give us a glimpse into the most extreme forms of interstellar interactions, including the so-called co-sphere phase. We hope to learn when and why collisions occur by studying the V838 Mon and similar collisions in detail. It is also important to know what kind of stars were formed as a result of such collisions, because it is suspected that many known stars were formed in this way, for example Betelgeuse or the star that exploded as supernova 1987A – added Dr. Tomasz Kaminsky.

The results of the research were published in the Journal of Astronomy and Astrophysics. The research team from Polish centers included: Tomasz Kamiński (CAMK PAN, Toruń), Romuald Tylenda (CAMK PAN, Toruń), Aleksandra Kiljan (University of Warsaw Astronomical Observatory), Mirosław Schmidt (CAMK PAN, Toruń), Krzysztof LisieckiUMK Institute of Astronomy (CAMK PAN, Toruń). , Toru), Adam Frankowski (CAMK PAN, Toruń) and researchers from the USA, India and Germany.