Brightest Supernova Ever Discovered Amazes And Confounds

Supernova 2015 L appears as a 17th magnitude blip of light in this photo taken last June. Its remote distance of 2.8 billion light years Not much to look at but that's onl
Supernova 2015 L a.k.a. ASASSN-15lh appears as a 17th magnitude blip of light in this photo taken last June. Its remote distance of 2.8 billion light years masks its tremendous brilliance. At the time this single stellar explosion was 20 times brighter than the entire Milky Way Galaxy. Credit: Joseph Brimacombe

Last June, the All-Sky Automated Survey for Supernovae (ASAS-SN — think “assassin”) discovered a faint flicker of starlight in an unremarkable galaxy in the far southern constellation of Indus the Indian. Hundreds of supernovae are discovered every year, but this one was different. Once it was determined the exploding star lay 2.8 billion light years from Earth or more than a thousand times farther than the Andromeda Galaxy, astronomers realized they had happened on the biggest supernova blast ever seen.

Type II supernova explosions involve the destruction of a massive supergiant star. Credit: ESO
A massive supergiant star at the end of its life collapses and explodes as a supernova. Infalling star matter can compress the core to create a fast-spinning, tiny neutron star. Credit: ESO

At peak brightness, if SN 2015L had been the same distance as Alpha Centauri, it would have shone nearly as brightly as the sun! To this day, it radiates more energy per second than all 300 billion stars of the Milky Way. So where does it fit in the scheme of stellar explosions? Astronomers still don’t know what powered such an enormous explosion, but they have ideas.

Normal supernovae are a big deal, but they pale next to the superluminous variety sometimes called hypernovae which shine 5 to 50 times times more brightly. ASASSN-15lh was several times brighter yet. Supernovae either occur in pairs of stars, where one star “feeds” its tiny, superdense companion white dwarf until the dwarf exceeds a certain weight limit and burns explosively or in a single supergiant star that depletes all the nuclear fuel in its core. Without heat and pressure to combat the force of gravity, the giant collapses and then rebounds in a titanic blast that blows the star to smithereens.

an unusual type of neutron star with an extremely strong magnetic field
Artist impression of a magnetar, an unusual type of neutron star with an extremely strong magnetic field. Credit: ESO/L. Calcada

To explain ASASSN-15lh’s super-bright light, it’s possible its core imploded with all the matter crunched into a fantastically compact, rapidly-spinning object about 10 miles across called a neutron star. If you could scrape it up, a thimbleful of neutron star matter would weigh about 1oo million tons.

During the collapse, the former star’s magnetic field (all stars have them) would have been crunched and intensified along with material in the star’s core to create a rare magnetar, a neutron star with an incredibly powerful magnetic field up to a trillion times that of the sun. As the magnetar spins, it gives off strong bursts of X-rays and gamma rays which may help to explain why this supernova is so doggone bright.

It's thought that a during a supernova collapse an even more compressed, denser star might be formed that could explain the brilliance of SN 2015L. A quark star
It’s thought that a during a supernova collapse an even more compressed state of matter might be created. Familiar neutrons and protons could be crushed down into their component pieces called quarks, the tiniest bits of matter known. The star is called a “strange” quark star because some of the up and down quarks, of which neutrons are made, are converted into “strange” quarks. The word “strange” is just a name and not a quality. Credit: NASA/Chandra

Or not. It’s already cranked out more energy that even current models of magnetars predict, leading some astronomers to consider other possibilities, including a strange quark star, a hypothetical stellar remnant made of quarks, the tiniest of things that compose the neutrons and protons in the nucleus of an atom.

Somehow, we’ve traveled from supergiant stars to quarks — nature’s way of telling us that the behavior of the biggest things in the world depends upon their tiniest parts.

For more details on this unique star, check out the scientific paper.

11 Responses

  1. Les

    Do you have any information about a planetary line up on jan 20th? Will that cause any time of interruptions for us? Does that mean anything that all the planets are lining up ?

    1. astrobob

      Hi Les,
      Yes, starting late this month, Mercury, Venus, Mars and Jupiter will be strung out across the morning sky from the eastern horizon to the western. This happens now and again over the years and is normal.

    2. caralex

      Short answer, Les – no. Planetary line ups are common, given that all the planets are orbiting the sun and are bound to coincide in one part of the sky or other at any given time. Explore this interesting website for an idea of the vast scale of the solar system…see how long it takes you to scroll from one planet to the other. As you can see, the planets are so far apart that there’s no way any one of them could negatively affect the earth:

    1. astrobob

      Hi Michael,
      I’m sorry, but it’s much too faint to see in an amateur telescope. It’s only visible now in long-time exposure photographs using larger telescopes. It’s also too far south to see from Arizona.

  2. Mark

    They are on their way here via Solar sail driven by a Trillion Terra-watt laser, won’t arrive in our life time though. Rats.

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