Un-nova

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Artist's impression of a dark supernova. Source: NASA

The term un-nova or unnova describes the direct gravitational collapse of a massive star into a black hole without emitting electromagnetic radiation in the form of a supernova . Un-novae are also known as failed supernovae . This hypothetical event could explain the observation that the interstellar medium is less enriched with metals than would be assumed if all stars above eight solar masses explode in a supernova. Alternative names for Unnova are dark supernova or failed supernova.

requirements

After the nucleosynthesis of iron in its core, a massive star can no longer generate energy through further nuclear fusions , since the synthesis of elements beyond iron would be endothermic reactions that consume more energy than they generate. This means that there is no radiation pressure to prevent the star from gravitational collapse, and the nucleus collapses into a protoneutron star with the emission of neutrinos . A shock front runs through the atmosphere of the star , which gets stuck due to the dissociation of heavy elements.

If falling matter drives the protoneutron star over the Tolman-Oppenheimer-Volkoff boundary or if the neutron star loses sufficient thermal energy due to cooling and can therefore no longer avert the core collapse, the collapse can occur in a black hole. If the protoneutron star collapses very quickly into a black hole, the result can be a un-nova in which little or no electromagnetic radiation is emitted. However, these events are subject to great uncertainties because the equation of state of highly compressed matter is not exactly known.

Unnovae in red supergiants

The formation of a black hole from a red supergiant could lead to an explosion lasting 3–10 days with a luminosity of around 10 34  joules / s at a surface temperature of 10,000 K. Such an event is (Engl. As a failed supernova failed supernova ), respectively.

Even if a failed supernova has not yet been observed, there are two indications for such behavior:

  1. no red giants with more than 16.5  solar masses have been found as precursor stars in core collapse supernovae .
  2. the remains from the supernovae explosions are either a neutron star with 1.4 solar masses or a black hole with over five solar masses. This dichotomy can be interpreted as a sequence of failed supernovae.
  3. The supernovar rate is significantly lower than the expected value if all red supergiants ended up in a core collapse supernova

Other authors come to the result in their calculations that with the core collapse of red hypergiants a transient develops instead of a un-nova , which is more like a luminous red nova and matter with a speed of "only" 100 km / s instead of up to Emits 20,000 km / s.

Two composite images from the optical and infrared show N6946-BH1 before and after the eruption. Source NASA Hubble Space Telescope Institute

Alternatively, a failed supernova could initially resemble a supernova impositor . These bursts light up with a brightness of around 10,000,000 solar luminosities for a few days and are caused by a Supernova Shock Breakout . After that the juggler (English impositor) glows for a year with a tenth of the previous luminosity and develops a dust cover that leads to an increase in brightness in the infrared and a decrease in the optical. Meanwhile, the collapse has taken place inside the dust cover and as a result the bolometric brightness steadily decreases. The no longer detectable transient N6946-BH1 in the spiral galaxy NGC 6946 could have been a dark supernova.

Individual evidence

  1. ↑ CS Kochanek et al .: A Survey About Nothing: Monitoring a Million Supergiants for Failed Supernovae . In: Astrophysics. Solar and Stellar Astrophysics . 2008, arxiv : 0802.0456v1 .
  2. ↑ EVAN O'CONNOR AND CHRISTIAN D. OTT: BLACK HOLE FORMATION IN FAILING CORE-COLLAPSE SUPERNOVAE . In: Astrophysics. Solar and Stellar Astrophysics . 2010, arxiv : 1010.5550v1 .
  3. ↑ Hasan Yuksel, Matthew D. Kistler: The Cosmic MeV Neutrino Background as a Laboratory for Black Hole Formation . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1212.4844v1 .
  4. ↑ ANTHONY L. PIRO: TAKING THE "UN" OUT OF "UNNOVAE" . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1304.1539v1 .
  5. ↑ CS Kochanek: Dust Formation By Failed Supernovae . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1402.4812v1 .
  6. ↑ SM Adams, CS Kochanek, JR Gerke, KZ Staneki: The Search for Failed Supernovae with the Large Binocular Telescope: Constraints from 7 Years of Data . In: Astrophysics. Solar and Stellar Astrophysics . 2016, arxiv : 1610.02402v2 .
  7. ↑ Elizabeth Lovegrove, Stan Woosley: Very Low Energy Supernovae from Neutrino Mass Loss . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1303.5055v1 .
  8. ↑ SM Adams, CS Kochanek, JR Gerke, KZ Staneki: The search for failed supernovae with the Large Binocular Telescope: confirmation of a disappearing star . In: Astrophysics. Solar and Stellar Astrophysics . 2016, arxiv : 1609.01283v2 .