Mergerburst
Under Merger burst (from english Merger burst at about German fusion outbreak ) is understood in the astrophysics the brief illumination of a star as a result of fusing with a companion star .
Whether mergebursts is the mechanism for generating so-called bright red novas , or whether other models are also responsible for some outbreaks, cannot yet be answered on the basis of the available data.
theory
Star merger
The merging of two stars in a binary star system has long been regarded as the cause of rapidly rotating single stars of the type FK Comae Berenices . The eclipse-changeable contact systems of the W-Ursae-Majoris-Stern type are assumed to be forerunners . In these, the two stars in a binary star system have already come so close that they form a common shell . By friction of the smaller companion spiraling into the larger component and the implementation of the kinetic energy can lead to ejection of an expanding sleeve. The changed mass distribution may influence the shell burning in the newly formed larger star. Due to the different masses and the mass distribution in the binary star systems involved and depending on the orbit inclination , a series of breakout light curves can be modeled. The merger of two neutron stars represents an extreme case . This event is known as the kilonova .
Crash of a planet
A merger burst could also occur if a star and a planet were to merge . Hot Jupiter in particular are candidates for a merger burst. These gas planets are already in short-period orbits around their central star. The tracks can be unstable e.g. B. due to Darwin instability . The rate of merging within the Milky Way is estimated at 0.1 to 1 per year. The course of the eruption depends on the ratio of the densities of the star and the planet, since either the planet enters the star's atmosphere as an object and a stable mass flow is established from the planet to the star or the planet is torn apart by tidal forces before merging . An outbreak of brightness in the optical, ultraviolet and X-ray radiation range should be a consequence of the thermal radiation of the accretion disk as well as the interaction of jets with circumstellar material. The energy released during the crash may also be sufficient to ignite the deuterium burn in the star's atmosphere, and as a result, the brightness increases sharply within a few days, as observed.
When a brown dwarf collides with a planet, an outbreak with a smaller amplitude and duration could also occur. However, an eruption lasting only a few days has not yet been observed.
Alternative theory
An alternative hypothesis has also been proposed for the light curves of the merger bursts. Accordingly, an unrealistically high opacity is required for the observed period shortening before the outbreak , and the slow rise to maximum brightness takes too long for a merger burst. Instead, it could be the beginning of a contact phase in a binary star system, releasing a lot of material from one star into a common non-corotating envelope around the binary star. The binary star system with a smaller period therefore still exists within the common shell.
Examples
V1309 Sco
The bright red Nova V1309 Sco that erupted in 2008 is in a monitoring field of the OGLE experiment , so photometric data from the years before the eruption are available. During this period, there was an overcast light change with a period of 1.4 days. The change in light was typical for a contact system. The period decreased exponentially in the six years before the outbreak and the light curve was highly variable. In the year before the eruption, no more overcast light change was detectable. The total brightness of V1309 Sco increased continuously over the years, only to decrease by 1 mag in 2007 . In the following year the brightness only increased slowly, only to reach the maximum within a few weeks with an outbreak amplitude of 10 mag.
According to simulation calculations, the predecessor of the Red Nova was a binary star with a total mass of around 2 solar masses.
KIC 9832227
KIC 9832227 is a binary star system whose two components rotate around each other in just under 11 hours. The period of rotation decreases continuously. The merger of the two stars was initially predicted for 2022. However, new calculations including older measurements from 2003 and a discovered error in the documentation of a measuring point from 1999 refuted the prediction. When the event will occur is open again. The bright red nova should be visible to the naked eye from Earth for months.
V838 Mon
The V838 Mon eruption was discovered on January 6, 2002. A comparison with archive images showed that it must have taken place around January 1, 2002. The first outbreak was relatively unspectacular and comparable to the behavior of a star of the Nova type . A second outbreak was discovered on February 2, 2002. V838 Mon, in contrast to novae or supernovae, hardly lost any matter at high speed during this eruption , but instead expanded enormously and transformed into a cool supergiant with a diameter of over 1,560 million kilometers. From 2004 to 2006, the observations showed signs of a blue companion star. This is what the ever expanding envelope seems to have reached around December 2005. Finally, in October 2006, the shell reached dimensions in which the companion was completely swallowed.
SN 2009ip
A merger burst can also lead to eruptions, the luminosity of which significantly exceeds that of luminous red novae. The Supernova Impostor SN 2009ip could be the result of a merger of a supermassive star with a mass of around 100 solar masses and a massive star of around 30 solar masses. The time scales for this outbreak correspond to those of a merger burst like V838 Mon, but the luminosities are several orders of magnitude higher. However, the event could also have been caused by an unusual core collapse supernova or a large eruption of a luminous blue variable .
GW170817
GW170817 was the first time that astronomers could measure both gravitational waves and electromagnetic radiation from the same astronomical event. The event is interpreted as a kilonova, the collision of two neutron stars.
Individual evidence
- ↑ A. Savior B. Zhang, L. Siess, A. Levinson, A. Marom ,: The Planets capture Model of V838 Mon . In: Astronomical Society of the Pacific Conference Series . tape 324 , 2007, pp. 271 .
- ↑ BD Metzger, D. Giannios, DS Mirror: Optical and X-ray Transients from Planet star mergers . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1204.0796v1 .
- ↑ Ealeal Bear, Amit Kashi, Noam Soker: Mergerburst transients of brown dwarfs with exoplanets . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1104.4106v1 .
- ↑ Ondrej Pejcha: Burying a Binary: Dynamical Mass Loss and of Optically Thick wind Explain the Candidate Stellar merger V1309 Scorpii . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1307.4088v1 .
- ↑ R. Tylenda, M. Hajduk, T. Kamiński, A. Udalski, I. Soszyński, M. K Szymański, M. Kubiak, G. Pietrzyński, R. Poleski, Ł Wyrzykowski, K. Ulaczyk: V1309 Scorpii: merger of a contact binary . In: Astrophysics. Solar and Stellar Astrophysics . November 1, 2010, arxiv : 1012.0163 .
- ↑ K. Stepien: Evolution of the progenitor binary of V1309 Scorpii before merger . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1105.2627 .
- ↑ Karen Kinemuchi, To Pulsate or to Eclipse? Status of KIC 9832227 Variable Star , October 1, 2013 ,. arxiv : 1310.0544
- ↑ Abenteuer-Astronomie.de : "Rote Nova" 2022 in the swan surprisingly canceled . Retrieved February 11, 2020.
- ↑ Lawrence A. Molnar, Daniel Van Noord, Karen Kinemuchi, Jason P. Smolinski, Cara E. Alexander, Henry A. Kobulnicky, Evan M. Cook, Byoungchan Jang, Steven D. Steenwyk: KIC 9832227: A red nova precursor , American Astronomical Society Meeting 229, 2017, p. 417.04. bibcode : 2017AAS ... 22941704M
- ↑ International Astronomical Union Circular No. 7785
- ↑ International Astronomical Union Circular No. 7790
- ↑ International Astronomical Union Circular No. 7816
- ↑ bibcode : 2005A & A ... 434.1107M
- ↑ http://www.astronomerstelegram.org/?read=803
- ↑ http://www.astronomerstelegram.org/?read=966
- ↑ Noam Soker, Amit Kashi: Explaining the supernova impostor sn 2009ip as mergerburst . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1211.5388 .
- ↑ http://www.sciencemag.org/news/2017/10/merging-neutron-stars-generate-gravitational-waves-and-celestial-light-show