Supernovae in the Milky Way

The first recorded supernova in our Milky Way galaxy (or anywhere else, for that matter) was seen to blaze forth in the constellation Centaurus by astute Chinese astronomers in 185 AD. Including that one, only seven confirmed supernovae have been observed in our Milky Way galaxy, though thousands are discovered each year in other galaxies.

Supernova light reached Earth in AD 185, 393, 1006, 1054, 1181, 1572, and 1604. All seven of these events occurred before the invention of the telescope. Are we overdue for another supernova? Well, given this ridiculously small sample, we can endeavor to do some simple “statistics”. The shortest recorded interval between two Milky Way supernovae was 32 years between 1572 and 1604. The longest interval has been 613 years, between the supernovae of 393 and 1006 (assuming none went unnoticed). On average then (such as it is), we “should” have seen a Milky Way supernova around 1841, and using the longest interval of 613 years, we might be expecting one by the year 2217. Undoubtedly, some supernovae in the Milky Way have escaped detection because they lay behind thick interstellar clouds.

The big mystery to me is why are there no recorded supernova events prior to 185 AD? The earliest extant records of astronomical events go back at least as far as 2316 BC (a comet in the constellation Crater was recorded by Chinese astronomers), but in the intervening 2,500 years there has been no mention of anything that could be attributed to a supernova. Or has there? Some writings before and after 185 AD suggest possible supernovae, but until a supernova remnant is identified, we need to look for other explanations.

Here follows a table of the known observed Milky Way supernovae. Of course, other supernova remnants have been discovered in our Milky Way galaxy, but no record has yet been discovered describing these events. Many of them predate recorded history.

In the table below, you’ll note that these supernovae tend to lie close to the galactic plane (galactic latitude b = 0°)—not at all surprising considering that’s where most of the stars are.

Milky Way Supernovae confirmed to have been observed

M31, M33, and the Milky Way

We live within a small cluster of at least 54 galaxies (most of them small), given the unassuming name “The Local Group” by Edwin Hubble (1889-1953) in 1936. The largest of these, M31 (the Andromeda Galaxy) is a barred spiral galaxy 2.5 million light years from Earth.  The second largest galaxy in the Local Group is our Milky Way, a barred spiral galaxy whose center lies about 26,000 light years away in Sagittarius.  The third largest galaxy in the Local Group is M33 (the Triangulum Galaxy), a spiral galaxy (possibly barred) located 3.0 million light years from Earth.  There are no other spiral galaxies in the Local Group.

M31 and our Milky Way are moving towards each other, and will pass through one another (or at least graze: shall we call it star grazing?) in about 4 billion years.

M33, however, is only about 860,000 light years from M31.  Isn’t M33 in even greater danger of colliding with M31?  The answer is no, we don’t think so, because M33 appears to be orbiting M31.  M33’s eventual role in the Battle of the Titans remains to be determined.