Big News from Astronomy: Type Ia supernovas explained?

Articles on scientific research rarely make the headline slot on the New York Times website and articles on true astronomy (none of this going to the moon crap) show up once in a blue moon. So this article on a new finding about the origins of Type Ia supernovae is really something special. Having been an Astronomy major, this is very important to me and has woken me from my dormancy on this blog. So, here is my evaluation.

The article does a decent job of covering the main who, what, where, and even touches on the big picture stuff, but misses a few important things, which I will elaborate on here. Basically, it skips over the chain of reasoning of why this research on a particular phenomenon is important to cosmology. A couple of things to keep in mind:

1) There are two types of Supernovae, I and II. Type two are caused by the core collapse of enormous stars many many many times more massive than our sun. It is a brilliant death, responsible for the dispersion of heavier elements like iron and gold into the rest of a Galaxy. When you hear that humans are made of star dust, this is what they're talking about. Type I supernovae come from smaller stars that also explode, but for different reasons. Type Ia, the subject of this article, only involve white dwarves, which are the remnants of large stars at the very end of their lives. Without either of the interactions - accreting matter from a partner or colliding with another white dwarf - a white dwarf would just burn faintly for several billion more years. (Fun fact: the universe is not old enough for the first white dwarfs to have burned out. So the first star to become a white dwarf is presumeably still burning out there, an ember in the cosmic fire pit.) Once a white dwarf gains a certain amount of mass it will invariably go Type Ia and explode.

2) There are two types of galaxies relevant to this article. Spiral galaxies are the pretty ones, with magnificent arms and dazzling central bulges. Most likely have a supermassive black hole at the center. Elliptical galaxies can be huge, but don't have an immediately visible structure. They are mostly amorphous and bloblike.

3) The distance ladder. A lot of astronomy deals with determining distances. In many cases, unless you know the distance to something, there isn't a lot you can say about it. The first step is parallax - you take measurements of a star's position compared to other stars from opposite sides of the sun and see how it changes. It's like putting your finger out at arms length and looking at it with only one eye, then the other. Using trigonometry, you can determine how far away it is. The next step is called a standard candle, which is where we come back to the article. Type Ia supernovae are considered standard candles: they have remarkably consistent in brightness. If you observe one going off, you can see how bright it APPEARS to be on Earth, and then find the distance to it (since light gets dimmer the farther away it is in an inverse square realationship).

In case you missed it, the main thrust of the article is that this research casts a bit of uncertainty on the study that claims "dark energy" is making the universe expand faster and faster. We've known for almost 100 years that the universe is expanding. Recently we've thought the expansion is accelerating. The team that claimed this used Type Ia supernovas as their standard candle. The main question now is: do collision-based Type Ia supernovae produce exactly the same light curve as a Ia explosion where a white dwarf slowly gains mass? If you're slowly gaining mass, you start the chain of events leading to explosion almost the moment you hit a mass 1.4 times the mass of the Sun. But how does it work when you have one White Dwarf that is the same size as the sun and it collides with a WD that is .8 solar masses? You will reach the limit, but is it the same explosion?

The people who have the dark energy claim have countered that this new study doesn't affect their research since it looked at Ia supernovae in Elliptical galaxies, while the dark energy study used supernovae in Spiral galaxies, which are thought to be the kind that gain mass slowly and predictably. This leaves the question "what kind of supernovae have we been looking at for the last several decades?" Accretion seemed to be the best explanation for Type Ia supernovae, since the odds of two white dwarfs colliding is so small. Then again, on astronomical scales, we should expect that it will happen, in many instances. Whether or not we can see them is another question.

So there is your crash course in Cosmology. This dark energy stuff is a big question. We really want to know whether it exists or not, since we have almost no idea what it could be. This new study, like all really great work, opens up all sorts of new interesting questions. One hundred new PhDs will be granted in the coming years on the topic of determining the similarities or differences between the collision and accretion Type Ia supernovae.