New Supernova Is Discovered by Young Citizen Scientist
Caroline Moore's discovery has made experts question how stars die
There is no age restriction on the chance to make a significant contribution to our understanding of the universe. Caroline Moore, a 14-year-old from Warwick, N.Y., has made such a mark on astronomy with the discovery of Supernova 2008ha. Not only is she the youngest person to discover a supernova, but this particular supernova has been identified as a different type of stellar explosion.
"It's really a strange supernova," said Moore. "A supernova is a huge explosion deep in the core of a star, whereas a nova is an explosion on the outside surface of a star. Of Supernova 2008ha she says, "It's somewhere between a supernova and a nova. So it's not nearly as big as the explosion of a supernova."
Alex Filippenko, an NSF-funded researcher at the University of California at Berkeley, has sought to understand progenitor stars (stars that produce supernova explosions), explosion mechanisms, and nucleosynthetic products of different types of supernovae. By studying the spectra of exploding stars, he can determine what kinds of explosions have occurred. Knowing this tells him how the stars explode and what kinds of chemical elements they should produce.
Filippenko received a three-year NSF grant that has funded supernova research involving discovery and rates of supernovae in nearby galaxies, and detailed studies of many of these events.When Moore's findings of what she suspected to be a supernova were published, Filippenko was naturally intrigued.
"She reported it as a supernova candidate, and our team is interested in any supernova candidates," said Filippenko. "I think that supernovae are a tremendously interesting aspect of astronomical research these days--not only did they lead to our existence, but they provide these luminous beacons which we can see billions of light years away, allowing us to probe the expansion history of the universe."
There are two main types of supernova: Type Ia and Type II, both producing powerful explosions.
A Type Ia supernova originates from an exploding white dwarf star--a kind of stellar cinder. When a white dwarf star is gravitationally bound to another star, the white dwarf can steal material from its companion star, growing in mass. The material piling up on the surface of the white dwarf can get hot enough to ignite nuclear fusion, which produces a burst of energy from the star in an explosion. This is what is known as a typical "nova," with the white dwarf star flaring up in brightness for a short period of time and then returning to its former state.
If too much matter piles up on the surface of the white dwarf star, it becomes unstable and the white dwarf itself explodes, forming what is called a Type Ia supernova. Because of the way Type Ia supernovae occur, they all have almost the same luminosity. No matter where they happen in the universe, when astronomers see one, they know how bright it should be in an absolute sense.
The other type of supernova (Type II) is called a core collapse supernova. This happens with very massive stars at the end of their lives, when the iron core of the star collapses. The pressure inside the star cannot hold it up anymore against gravity. The core collapses inward and becomes part of a black hole, while the outer parts of the star explode outwards, forming the supernova that we observe on Earth.
"Because Supernova 2008ha is faint in appearance, it does not fall directly into either category, raising questions," said Filippenko. "Supernova 2008ha was more powerful than a typical nova or even the brightest nova that we know of, so it was sort of a supernova, but wasn't as powerful as a genuine supernova. We think that it may have been some sort of intermediate object, really a new class."
A new class of stars?
Moore's discovery is exciting because Filippenko and his team really don't know what happened. The spectrum of the explosion shows that very little radioactive nickel was produced, a signature of a Type II supernova. But Supernova 2008ha is less luminous than that expected for the Type II supernova.
"We think it is more closely related to the Type Ia, that is, the thermonuclear runaway of a white dwarf at or near the Chandrasekhar Limit," said Filippenko, referring to a crucial measurement astronomers use to analyze the evolution and demise of stars. "We think, in this case, the whole white dwarf didn't obliterate itself, only part of it went off. Now we know of such a phenomenon; it's called a nova, where the thin skin on the outskirts of a white dwarf goes off in a bang and produces a luminous thing, but not as luminous as a supernova."
Filippenko has suggested that Supernova 2008ha is just the start of the exploration of low-luminosity supernovae. In 2002, Filippenko and his team began to suspect there might be a new class of supernovae, a class that might be related to what is seen for Supernova 2008ha. Moore's discovery has pushed them in a new direction of considering how a star can explode.
"Where the white dwarf went off as a nuclear explosion, the outer 10 or 20 or 30 percent of the white dwarf's mass participated in the explosion and got ejected, and the rest got left behind," Filippenko surmised.
Moore's discovery has made experts question how stars die, since the current supernova models fall short of explaining the low luminosity and low energy of 2008ha. The discovery of her supernova has also shown how amateur astronomers can make a difference.
Astronomy is for everyone
Regardless of what experts find, Supernova 2008ha is just the beginning for Caroline Moore. In this year, the International Year of Astronomy, Moore is hoping to encourage more people to become involved in astronomy at the North Eastern Astronomy Forum (NEAF), an annual astronomy forum and telescope show.
"I work with NEAF and work with kids there; we teach them about astronomy and scientific experiments. This year at NEAF our goal is to get 1,000 kids to come, and I'm hoping to make that possible," said Moore. "We really try to not get just kids involved, but the public involved in astronomy."
Alex Filippenko also views astronomy as a democratic process in which anyone, regardless of age and experience, can make a significant impact.
"Astronomy is there for everyone. Many people simply enjoy it and enjoy learning about the discoveries of astronomers and that's great. But it's wonderful that ordinary people who have ordinary jobs not in the sciences, can also contribute to actual research," said Filippenko.
Supernova 2008ha has spurred the search for other low luminosity supernovae and Moore is starting her own journey and encouraging people to explore the fields of astronomy and science.
"If you are interested in astronomy, I would say there is no need for you to go out and buy an expensive telescope or anything. Just join a local astronomy club. If you have a pair of binoculars, that's a great way to start. If you have a telescope shoved inside your closet, take it out and start learning how to use it. Don't think you've got to learn to use it by yourself, there are lots of people who are willing to help," said Moore.