A lot of internet activity has surrounded the discovery on May 19 of Supernova 2023ixf in the “Pinwheel Galaxy” M101. And deservedly so, as this is the closest supernova to us that has occurred in the last 5 years. It is also bright enough at magnitude 11 to be visible in the Northern Hemisphere in small telescopes! For more on this discovery see this article
Now only about 5 days before SN 2023ixf blew up, another star went through it’s last moments of life and subsequently blew up in another galaxy about three times as far away from us as M101. Consequently this supernova is not as bright as the one in M101 but it occurred in the fascinating interacting galactic pair of NGC 4568 and 4567. The “host” galaxy is NGC 4568 which is the larger of the two as you can see. These galaxies are in the process of colliding and merging with each other, as studies of their distributions of neutral and molecular hydrogen show, with the highest star-formation activity in the part where they overlap. However, the system is still in an early phase of interaction (courtesy Wikipedia). These types of high energy galactic processes are known “hotbeds” of supernova activity.
On May 12, I started imaging this region not for the purpose of supernova discovery at all but mainly because it’s a fascinating example of a galactic merger that we can actually see happening! About two days later I received a bulletin from one of the online spectroscopy groups about this new supernova. Unfortunately my high res spectroscopy set up has a mag limit of about 9-10 so I was not going to be able to capture a spectra of it, but I was already imaging it serrendipitously! I checked my first images of the galaxy pair but unfortunately there was no evidence of a star there, so I cannot claim discovery. I had to skip a couple of nights due to weather and this is the period when the actual discovery happened. Close but no cigar!
The discovery is credited to the All Sky Automated Survey for Supernovae based out of Ohio State University
The short animation shown here was created with two uncalibrated raw 15 minute frames I took about 12 days apart, from two days prior to discovery until 10 days after. The actual day of the discovery I could not image due to weather!
Some Supernova FAQ’s:
What is a Supernova?
Supernovae are massive stellar explosions that result in a visible stellar object where none was seen before. This is probably the the biggest explosion in the universe we can observe visually. There are currently two types:
Type Ia supernovae occur in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf, which is the small remnant of a star that has exhausted it’s fuel. The other star can be anything from a giant star to an even smaller white dwarf. If a white dwarf gradually accretes mass from a binary companion, or merges with a second white dwarf, the general hypothesis is that a white dwarf’s core will reach the ignition temperature for carbon fusion as it approaches the Chandrasekhar mass. Within a few seconds of initiation of nuclear fusion, a substantial fraction of the matter in the white dwarf undergoes a runaway reaction, releasing enough energy to cause the supernova explosion. The Type Ia category of supernova produces a fairly consistent peak luminosity because of this fixed critical mass at which a white dwarf will explode. Their consistent peak luminosity allows these explosions to be used as standard candles to measure the distance to their host galaxies: the visual magnitude of a type Ia supernova, as observed from Earth, indicates its distance from Earth. (courtesy Wikipedia)
Type II supernovae result from the rapid collapse and violent explosion of a massive star. A star must have at least eight times, but no more than 40 to 50 times, the mass of the Sun (M☉) to undergo this type of explosion. Type II supernovae are distinguished from other types of supernovae by the presence of hydrogen in their spectra. They are usually observed in the spiral arms of galaxies. Depending on initial mass of the star, the remnants of the core form a neutron star or a black hole
Both SN 2023 ixf and ijd have been determined to be the Type II variety.
How common is a supernova?
In any one galaxy we can expect maybe a couple supernovae per century. But thankfully the universe is filled with billions of galaxies so from Earth we are able to detect a few hundred per year!
How are supernovae discovered?
Usually supernovae are discovered with telescopic surveys of the sky such as the one that detected SN 2023 ijd. Robotic telescopes are commonplace now and cover a huge amount of space in a short time. Multiple galaxies are targeted in a single night and short exposure images are obtained and compared to previous sky surveys to see if there is any change. The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, uses X-ray to investigate supernovas and young nebulas to learn more about what happens leading up to, during, and after these spectacular blasts.
What is learned from studying supernovae?
As mentioned above the Type Ia supernova can be used to measure galactic distance. We have also learned that stars generate chemical elements needed to make pretty much everything including life as we know it. When stars explode these elements are distributed throughout space.
Hope you learned something about supernovae!
Thanks for reading!
DrDave