A mysterious supernova caught in Kepler’s last days

The Kepler Space Telescope mission ended in October, but the analysis of its latest data continues to reveal a wealth of information, not only for researchers looking for new exoplanets, but also for supernovas specialists.

Images taken on February 4th by the Kepler Space Telescope revealed unusual details from the explosion of a star in a galaxy more than 170 million light-years away from us.

Although it is the fourth such explosion to be observed by Kepler, Kepler is also the closest to being captured by the telescope. Now, the images of the supernova, now named SN 2018oh, showed that the explosion did not unfold as expected.

These observations, far from being disappointing to scientists, may help to better understand the mechanisms of Type 1a supernovae, whose blast serves as a reference point for astronomers to measure distances across the Universe.

The phenomenon recently led to the publication of three scientific articles in The Astrophysical Journal and The Astrophysical Journal Letters ( first article , second article , third article ).

A lighthouse in the interstellar void

Supernovas are often associated with the life of massive stars that collapse on themselves and are destroyed in a gigantic explosion.

This is not exactly what happens with a type 1a supernova. These explosions occur in binary systems, where two stars are in orbit around each other and one of whose partners is a white dwarf, a star-shaped residue similar in size to the Earth, but also dense as our Sun.

The gravity force of the white dwarf may be powerful enough to cannibalize its neighbor and steal matter by accumulating it on its surface. When this coating reaches a critical point, this material ignites like a hydrogen bomb. The star then explodes producing a burst of visible light across the Universe.

Since these explosions always occur according to the same parameters, the brightness of Type 1a supernovas serves as a reference point for astronomers when it comes time to estimate the distance of distant galaxies.

Riddles in the dark

Despite the importance of the phenomenon, researchers are not yet certain of the mechanism that leads to this explosion or the nature of the star cannibalized by the white dwarf.

It is for this reason that astrophysicists deem it essential to capture the first moments of these explosions. SN 2018oh was first captured by robotic telescopes that are part of the program called “Automated Sky Record for Supernovas”, which is short for ASAS-SN (pronounced assassin).

By pure luck, this explosion occurred in a segment of the sky scanned at the same time by Kepler, whose instruments designed to capture the tiny variations of light generated by exoplanets have yielded unparalleled data of the explosion.

Normally, the brightness of these supernovas gradually increases for three weeks before gradually fading. However, from its first moments, the brightness of SN 2018oh has increased at a much higher rate than expected in an explosion of this type.

In addition to this two-fold increase in brightness, SN 2018oh has become three times brighter than other supernovas of the same type.

Although researchers can not yet explain this behavior, they already have several hypotheses, ranging from an unexpected interaction between the explosion and the nearby star to the presence of rare radioactive material within the late dwarf white.

The observation of SN 2018oh in the coming months should allow researchers to find an answer to their question and better understand the nature of the stars that are accomplices to these spectacular explosions.

A hundred new exoplanets

The mystery of supernovas is not Kepler’s last contribution to science. A hundred new exoplanets are added to the already considerable legacy of the mission.

The discovery of these 104 new planets was announced in two waves: 44 last August and 60 others a few days ago. These new stars contain planets of all types, of which more than 34 are rocky worlds whose size is at most twice that of the Earth. The latter, however, would be uninhabitable due to the virtual absence of detectable atmosphere on their surface.

There is still a lot of data to analyze from Kepler’s latest observations. These analyzes will be followed by new observations by his successor, the TESS space telescope, whose first months of activity have already revealed a large number of new unknown worlds.

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