50 Fun Facts About Supernova

What is a supernova?

For a few weeks its peak brightness can rival an entire galaxy before it fades away.

Which two kinds of object can a supernova's progenitor collapse into?

Alternatively the star is completely destroyed, leaving only a spreading nebula of debris.

On average, how often is a supernova expected in the Milky Way?

Despite that, none has been seen in our galaxy since Kepler's in 1604; dust probably hid a couple since.

What was the last supernova observed in the Milky Way itself?

Kepler watched it from its peak on 17 October 1604 until it faded from naked-eye view a year later.

In which satellite galaxy of the Milky Way did SN 1987A explode?

It was the closest supernova of the telescopic age and was studied in unprecedented detail.

What kind of star was SN 1987A attributed to?

That was a surprise, since red supergiants were expected to be the usual core-collapse progenitors.

Which two astronomers coined the word 'supernova' in lectures in 1931?

Knut Lundmark used 'super-Novae' in print in 1933 and may have coined it independently; the hyphen was gone by 1938.

The Latin word 'nova', from which supernova derives, means what?

It refers to what looks like a temporary new star; the 'super-' prefix separates these blasts from far fainter ordinary novae.

What was the first widely recorded supernova, seen in the constellation Lupus?

Observers in China, Japan, Iraq, Egypt and Europe all described it.

What did the supernova that Chinese astronomers recorded in AD 1054 leave behind?

A 2021 study made it more likely that this was a rarer kind of collapse from a relatively light star.

Who observed the supernova of 1572 in Cassiopeia?

Along with the star of 1604, it helped demolish the Aristotelian idea that the heavens beyond the Moon never change.

Cassiopeia A, a Milky Way supernova remnant from around 1680, is notable for what?

Its date was worked out from light echoes; the even younger G1.9+0.3, from the late 19th century, was also missed.

What was the first supernova observed with a telescope, in 1885?

At the time it was thought to be simply an unusually strong nova; the idea of a separate class came in the 1920s.

Who developed the modern supernova classification scheme, beginning in 1941?

The scheme sorts explosions by their spectra and light curves rather than by what caused them.

What is the most luminous supernova ever recorded?

It peaked at 570 billion solar luminosities in 2015, though some argue it was really a star being torn apart by a black hole.

Amateur astronomer Victor Buso made history in 2016 by catching what for the first time?

He was testing a camera from Rosario, Argentina, and the progenitor star was later found in old Hubble images.

Roughly how many supernovae were astronomers finding each year by the early 2020s?

Most are in distant galaxies; amateurs long played a big role by comparing galaxies against earlier photographs.

What does the SNEWS project use to give early warning of a Milky Way supernova?

The particles race out of the collapsing core hours before the light and are barely absorbed by galactic dust.

Under the IAU naming convention, what does SN 2003C designate?

After Z come pairs of lower-case letters, so the 367th of 2005 was SN 2005nc, and four-letter tags like SN 2021afdx now appear.

To which body are supernova discoveries reported for naming?

It sends out a circular carrying the assigned name: SN, the year, then letters.

What decides whether a supernova is classified Type I or Type II?

Hydrogen present means Type II; the Balmer series is the tell-tale in visible light.

A strong ionised silicon absorption line marks which subtype?

Type Ib shows strong neutral helium lines instead, and Type Ic lacks both.

What does the 'n' stand for in Type IIn?

The narrow spectral lines come from ejecta ploughing into a small dense cloud the star shed shortly before dying.

What feature gives Type II-P supernovae their name?

The brightness holds roughly steady for months as hydrogen in the ejecta recombines; II-L 'linear' types lack it.

What kind of star explodes as a Type Ia supernova?

It steals matter from a companion or merges with another white dwarf until runaway carbon fusion blows it apart.

What is the Chandrasekhar limit, the mass a non-rotating white dwarf approaches before it detonates?

In practice carbon fusion ignites within about 1% of the limit, before actual collapse begins.

Why are Type Ia supernovae so useful to cosmologists?

Their peak absolute magnitude of about -19.3 is remarkably consistent, so their apparent brightness reveals how far away they are.

Distant supernovae observed in 2003 appeared dimmer than expected. What did this support?

Being fainter than predicted meant they were farther away than a steadily expanding universe would allow.

Roughly how much brighter than the Sun is a normal Type Ia supernova at peak?

That corresponds to an absolute magnitude of about -19.3, with very little variation from one to the next.

The radioactive decay of which isotope powers a Type Ia light curve?

It decays to cobalt-56 with a six-day half-life, and the cobalt's slower decay keeps the ejecta glowing for months.

What is the half-life of cobalt-56, which controls the later light curve of a supernova?

SN 1987A's fade matched the 77.3-day half-life closely, confirming the radioactive-heating theory.

Which element's fusion in a massive star's core signals the end, because it can no longer release energy?

Once the iron core outgrows the Chandrasekhar mass, electron degeneracy pressure fails and it collapses in a fraction of a second.

How fast can a collapsing stellar core fall inward?

The inner core ends up around 30 km across at the density of an atomic nucleus.

In a core-collapse supernova, what carries away the vast majority of the energy?

About 10% of the star's rest mass goes into a ten-second neutrino burst; the light show is a minor side-effect.

Below roughly what mass will a star never collapse its core, ending as a white dwarf instead?

Stars of about 9 to 12 solar masses and up burn heavier and heavier elements in onion-like shells before collapsing.

What kind of object is thought to be the progenitor of most Type Ib and Ic supernovae?

Oddly, not a single Wolf-Rayet progenitor had been clearly identified before SN 2019hgp in 2022.

Which nearby, well-known red supergiant is on the list of core-collapse supernova candidates?

Antares, VV Cephei A, and blue giants Spica, Rigel and Deneb are also on the watch list.

Which luminous blue variable has already produced a 'supernova impostor' outburst?

Its Great Eruption in the 1800s mimicked a supernova but left the star intact.

What is the closest known candidate for a Type Ia supernova, about 150 light-years away?

No need to worry: its white dwarf may need 1.9 billion years to accrete enough mass to blow.

Per a 2003 estimate, how close must a Type II supernova be to destroy half Earth's ozone layer?

Reassuringly, there are no such candidates closer than about 500 light-years.

Elevated levels of which ions in Antarctic ice have been linked to the 1006 and 1054 supernovae?

Gamma rays from the blasts could have boosted nitrogen oxides in the atmosphere, which then froze into the ice.

Enrichment of which isotope in deep-sea Pacific rock has been read as a trace of past nearby supernovae?

The idea that supernova debris could leave metal signatures in rock strata was first floated in 1996.

Supernovae are a major source of elements ranging from oxygen up to which element?

Elements heavier than iron come from rapid neutron capture, though neutron star mergers may be the main factory for many of them.

Core-collapse supernovae eject larger masses of which light elements than Type Ia explosions do?

Type Ia blasts instead specialise in silicon and the iron-peak metals.

Besides making elements, what can a supernova's expanding shock wave do to nearby molecular clouds?

Isotope evidence suggests a nearby supernova may even have helped trigger the birth of our own Solar System 4.5 billion years ago.

Ken'ichi Nomoto predicted a 'third type' of supernova in 1980. What is it called?

SN 2018zd, reported in 2021, looked like the first confirmed example, from a star of 8 to 10 solar masses.

What is the expanding shell of gas and dust left behind after a star explodes called?

The Crab Nebula and Cassiopeia A are famous examples; such shells also accelerate much of the galaxy's cosmic rays.

The most luminous Type Ic supernovae are known by what name?

Their extra energy is thought to come from relativistic jets driven by a newly formed rotating black hole, which can also fire off gamma-ray bursts.

Magnetars left by exploding stars are leading candidates for producing which mystery signals?

These intense radio pulses typically last no more than milliseconds, and their origin is still debated.

How was the date of the Cassiopeia A supernova event worked out?

A second unrecorded Milky Way remnant, RX J0852.0-4622, was dated instead from temperature and the gamma rays of decaying titanium-44.