As it was widely reported last week, astronomer Steve Fossy of the University of London Observatory was teaching a class about the use of a CCD camera, pointing at a galaxy called M82 as part of a demonstration, when he was surprised to discover a stellar explosion known as a supernova. This is a galaxy not too terribly far far away, which is good since it offers astronomers a reasonably close vantage point and gives amateurs the chance to see it too.
Within hours, news outlets were reporting that astronomers were “stunned” or “gaga”.
The more detailed stories explained that this is a type 1a supernova – a phenomenon that starts with an already burnt-out star known as a white dwarf. The details of how and why these objects occasionally explode remains under investigation. Type II supernovae come from the collapse and death of massive stars. For those of us old enough to remember it, supernova 1987a was a type II.
Scientists have been using type 1a supernova explosions to calibrate distances in the universe. Since they are fairly uniform in brightness, they are referred to as “standard candles”. They were used for the Nobel-winning discovery that the expansion of the universe is accelerating.
Here’s National Geographic online: Nearby Supernova Has Astronomers Going Gaga.
Readers are told that this explosion happened 12 million light years away, but we get little guidance in understanding what this distance means. Most non-astronomers would consider that a rather long distance. Some perspective would help. How many light years across is our Milky Way? And how many of our neighboring galaxies lie within a 12 million light year radius? How far away was 1987a?
CNN.com featured a piece by astronomer Meg Urry, headlined Cosmic Wow. A Rare, Exploding Star!
There’s a bit of perspective on the rarity of this event and why people are so excited:
Type Ia supernovae have happened in our galactic neighborhood only three times in the last 80 years. Like astronomers around the world, we were excited to be at a world-leading telescope, where we could collect new information about this rare event.
The new supernova, SN2014J, is 11.4 million light-years from Earth, a mere stone's throw in cosmic terms. The previous record-holders were found in 1937 (14 million light-years away) and 1972 (16 million light-years away).
Again, even more perspective would help readers understand why this seemingly long distance is just a stone’s throw. And readers need something more explicit to grasp how rare this event is. How far away can 1a’s be seen and how often are they observed? How often do they occur on a typical-sized galaxy?
At Slate, Bad Astronomer Phil Plait has not one but two exclamation marks in his headline: Kaboom! Nearby Galaxy M82 Hosts a New Supernova!
His story has an interesting section on the open questions surrounding the sequence of events that lead to these explosions:
Astronomers are still trying to figure out exactly what happens in a Type Ia explosion, but there are three competing scenarios. Each involves a white dwarf, the small, dense, hot core left over after a star turns into a red giant, blows off its outer layers, and essentially “dies.” One scenario is that the white dwarf is orbiting a second star. It siphons off material from the star and accumulates it on its surface. Eventually this material gets so compressed by the huge gravity of the white dwarf that it fuses, creating a catastrophic explosion that tears the star apart.
Another is that two white dwarfs orbit each other. Eventually they spiral in, merge, and explode. The third, which is a recent idea, is that there are actually three stars in the system, a normal star and two white dwarfs. Due to the complex dance of gravity, the third star warps the orbits of the two dwarfs, and at some point they collide head-on!
This is good, except for the unnecessary exclamation point. Here's the part about the distance:
M82 is pretty close as galaxies go, less than 12 million light years away. That means we have an excellent view of one of the biggest explosions in the Universe, and we’ll be able to study it in great detail!
Another exclamation mark? It's not helpful. What would help here is a comparison so we can see why 12 million light years is considered close in this case.
Arstechnica used a refreshingly sane headline: After bright explosion, astronomers rush to study new supernova.
There’s some helpful background here on type 1a explosions:
Type 1a supernovae are triggered either by the explosion of white dwarfs that accrete too much matter and exceed their maximum stable mass, or by the collision of two white dwarfs. (That's as opposed to core-collapse supernovae, which are the explosions of stars much more massive than the Sun.) Because they all explode in very similar ways, Type Ia supernovas are "standard candles": objects that can be used to measure distances to very distant galaxies. The use of them to track the expansion of the Universe was recognized by the 2011 Nobel Prize
Here are a few other questions that would be fascinating to pose to astronomers, or to answer yourself if you are an astronomer/science writer:
Will scientists be able to use this rare event to refine their understanding of this type of supernova and improve its use as a standard candle?
What else do astronomers hope to learn? Will this help them get a better handle on which of the proposed mechanisms led to the explosion?
How often do these explosions happen? If they are indeed rare, how have scientists managed to use them to measure the expansion rate of the universe?
How often do 1a explosions occur in our galaxy? What would it look like if such an event occurred?
The stories I’ve seen so far have spent considerable space telling us that astronomers are excited but offering little in the way of showing us why, either with examples of what could be learned or illustrations of the rarity and proximity of this event. Then readers could share in the excitement.
Another quibble: several authors said that observations of type 1a supernova explosions led to the discovery of dark energy. This is more or less true, but won’t make sense to lay readers without several logical links. What astrophysicists say is that a series of type 1a supernova observations allowed them to measure the expansion rate of the universe and discover that it’s accelerating. They didn’t expect it to be accelerating. They don’t know why it’s accelerating. They proposed that there must be some kind of hitherto unknown energy, which they term dark energy as a sort of place-holder. It’s called dark energy because they don’t know what it is. It may sound cool to say type 1a supernova explosions led to the discovery of dark energy, but without some explanation of the connections that lead from point a to point b, this risks leaving some readers in the dark.
Cosmology is so mind-blowingly interesting that it’s a shame some people think they’re not smart enough to grasp it. The fault lies not with the readers but with the explainers.
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