When stars explode, they generate light that you can see across the universe. But these events, called supernovas, are not just pretty to look at. They also are useful scientific tools to help researchers measure cosmological distances and speed, according to Space.com columnist Paul Sutterin his latest episode of "Ask A Spaceman."
In Episode 8 of the Facebook Watch series, Sutter talks about Type 1a supernovas, a particular kind of star explosion. These happen when white dwarfs — the burnt-up shells of stars similar to our sun — accumulate a certain amount of gas from a normal companion star. Once the white dwarf acquires a certain mass of gas, it explodes.
These explosions tend to be pretty similar, with only tiny variations, Sutter explains. And that makes them useful for figuring out stellar distances. Astronomers use a measure called luminosity, which refers to the intrinsic brightness of an object. Type 1a supernovas have the same luminosity, so any changes in apparent brightness are mainly due to their distance — how far or how close they are to Earth. [Know Your Novas: Star Explosions Explained (Infographic)]
Supernovas not only tell us how far away they are located, but they can also provide a measure for how fast the universe is expanding. Or as Sutter puts it, "It's almost like making a growth chart for a kid, but for the whole, entire universe."
When a Type 1a supernova explodes, astronomers can see what kinds of elements were inside the star before it exploded. They use a technique called spectroscopy, which (simply speaking) tracks the elements in the explosion by looking at the wavelengths of light they produce. This is possible because each element produces a distinctive set of wavelengths.
As Sutter explained in past episodes — such as this one about the universe's "baby picture" – the universe is expanding over time. Objects that are moving away from us will have their light stretched into the red side of the spectrum, which is known as "redshifting." Accordingly, the elements in the supernova will also have their signatures redshifted. The degree of that redshift shows how fast the supernova is moving away from us.
Astronomers are interested in learning about the universe's expansion rate because it tells us more about the nature of dark matter and dark energy, which are believed to make up most of the universe. Trouble is, dark energy and dark matter cannot be sensed through conventional instruments. Instead, astronomers measure dark matter by its gravitational effect on other objects, such as bending light in space, and dark energy by how it drives the universe to expand.
"Ask a Spaceman" episodes are released weekly on Wednesdays at 12 p.m. EDT (1600 GMT), so like its Facebook page or check back later to see more. Sutter also responds to reader questions in every episode. Check the page to learn more about past topics the show covered, such as the Big Bang, Pluto and galaxy collisions.
Sutter is a cosmologist at Ohio State University and chief scientist at Columbus Ohio's Center of Science and Industry. He has a long-running podcast, also called "Ask A Spaceman." You can catch all past episodes of that podcast here.