#type 2 supernova

[zespaceblog]

When a Star Explodes

We know a fair bit about how stars end their lives, the various different types of Supernova that can occur as a result, and space is full of the nebula of such events.

Above, Supernova 1987a, the last visible supernova in our neighbourhood, the large Magellanic clouds, and it gave us a chance to watch the remnants expand and form the hourglass shape in space, and better understand the aftermath of these violent events.

But one thing we've not seen, is a star in the lead up to a supernova, and then finally the supernova event, that was until SN2020tlf in the galaxy NGC 5731 occurred, literally, while we were watching.

The galaxy isn't close to us, in fact, it's 120 million light years from us, but we happened to be observing it closely when the supernova occurred.

Pouring over the collected data, for the very first time, it was noted that the star increased in brightness substantially in the lead up to the event over a period of several months. This is the first hint that type 2 supernova's (when a red giant gravitationally collapses due to failing fusion pressure from the core) brighten and not dim.

You may recall not so long ago all the conversation about the supergiant Betelgeuse and the sudden dimming and if this was the lead up to a supernova event, truth was, nobody alive had ever witnessed one and so we really had no way of knowing if it was, even if the most likely theory of dust obscuration turned out to be what the cause was.

So if other red giants follow suite, it looks like we'll get a few months warning of the event as the star brightens up as the collapse begins, it also gives astrophysicists a tonne of data to model collapse theories on, to see if we can better understand the processes that are going on.

Source : https://www.space.com/supernova-observations-what-happens-before-star-explodes

[wigmund]

From Earth Science Picture Of The Day; February 10, 2014:

Newly Discovered Supernovas in NGC 3448 and M82 Photographers and Summary Authors: (Top Image) Patrick Wiggins; (Bottom Image) Kosmas Gazeas

Top Image: In mid January I was lucky enough to discover a supernova -- SN 2014G. The G indicates it’s the seventh supernova discovered in 2014. It was found in galaxy NGC 3448 while observing from my home observatory near Salt Lake City. The pre-discovery image I used to compare with the SN 2014G image was acquired on January 6, 2014. The actual date of the discovery was January 14, 2014 at 07:36:02 UT, when a nearly full Moon brightened the sky. NGC 3448 is about 78 million light years away in the direction of the constellation Ursa Major. Light from this Type II supernova explosion that’s just reaching Earth now started its journey when dinosaurs roamed the Earth. This supernova is far too faint to be seen with the naked eye -- a fairly large telescope must be used.

Bottom Image: Shown at bottom is a Type Ia supernova (SN 2014J) that was also discovered in mid January in the direction of Ursa Major, but this exploded star is in the Cigar Galaxy (M82), some 12 million light years distant. Its discoverer is Steve Fossey of University College London. SN 2014J is evidently nearer to us than any other Type Ia supernova sighted in the past 42 years. Though this supernova is relatively nearby, it can't be seen with the unaided eye.

[joerosewood]

Stars with at least nine solar masses of material evolve in a complex fashion.[62] In the core of the star, hydrogen is fused into helium and the thermal energy released creates an outward pressure, which maintains the core in hydrostatic equilibrium and prevents collapse.

When the core's supply of hydrogen is exhausted, this outward pressure is no longer created. The core begins to collapse, causing a rise in temperature and pressure which becomes great enough to ignite the helium and start a helium-to-carbon fusion cycle, creating sufficient outward pressure to halt the collapse. The core expands and cools slightly, with a hydrogen-fusion outer layer, and a hotter, higher pressure, helium-fusion center. (Other elements such as magnesium, sulfur and calcium are also created and in some cases burned in these further reactions.)

This process repeats several times; each time the core collapses, and the collapse is halted by the ignition of a further process involving more massive nuclei and higher temperatures and pressures. Each layer is prevented from collapse by the heat and outward pressure of the fusion process in the next layer inward; each layer also burns hotter and quicker than the previous one—the final burn of silicon to iron consumes its fuel in just a few days at most.[63] The star becomes layered like an onion, with the burning of more easily fused elements occurring in larger shells