Monday, January 25, 2010

A Star Class is Born

Hold it right there, star. Trying to become a black hole, are ya? Well, not so fast. It's possible that as you begin to collapse and squeeze the subatomic particles at your core, the squarshed quarks could begin to radiate neutrinos and stop that collapse, leaving you stuck as a dense, nearly invisible lump for millions of years. Yeah, those tiny little quarks are real tough when you get a bunch of them together.

Scientists have proposed that there is a new, exotic type of star living in our universe that we haven't seen yet. The so-called "electroweak stars", if they exist, will be difficult to detect because they mostly emit neutrinos - subatomic particles which, for the most part, don't interact with ordinary matter.

[Image: "Electroweak" stars may recreate the conditions of the big bang in an apple-sized region in their cores (Illustration: Casey Reed, courtesy of Penn State)]

When massive stars run out of fuel to burn, they expand into a supernova and then begin to collapse, eventually compacting into black holes. Smaller stars, like our sun, collapse and may leave behind dense cores called white dwarfs but will never form a black hole. An "electroweak star" may prevent the supernova of a massive star from collapsing down into a black hole. It does this because of electroweak burning - essentially the transition of quarks into leptons, namely neutrinos.

As the dying star tries to collapse, a very large amount of mass may be pressed into an incredibly small area (the mass of two Earths into the size of an apple!). It takes this incredible pressure, and the pressing of a great deal of mass into a very small area, to make this electroweak burning occur. Instead of exploding into a great supernova or collapsing into a black hole, the star would live the rest of its life mostly invisible to us. Because neutrinos don't interact with regular matter (for the most part) they are very difficult to detect.

These electroweak stars may sound a bit like quark stars, which are thought to exist in the core of neutron stars. Neutron stars are incredibly dense, and at their cores, scientists believe the neutrons break down into their smaller parts - quarks. But the electroweak stars the density would be even greater, causing the distinction between two of the four fundamental forces - the electromagnetic and weak forces - would break down. Without this distinction, the quarks in electroweak stars would radiate neutrinos.

The electroweak stars are, for the moment, purely theoretical. Scientists who study our universe can use what we can see to make guesses about what we can't. They gather information about our surroundings, infer laws based on those observations, and come up with a models of the universe. The models aren't always perfect, but sometimes they lead to new discoveries. To better understand this, imagine you are standing in the middle of a house (lets say, in a hallway on the second floor). You are trying to make a drawing of what the entire house looks like, even though you can't see all of it. You would know quite a bit about the structure of the house immediately around you. If you couldn't see inside one room, but could see daylight coming out of it, you could reasonably guess that the room had a window. If you heard a door close and then saw someone enter your area wearing a rain coat, you could infer where the front door is.

In a similar way, scientists used the standard model to study the phenomenon of electroweak burning, in which quarks (the subatomic particles that make up protons, neutrons and electrons, which in turn make up atoms) turn into different subatomic particles called leptons. In normal stars, lighter particles like hydrogen can fuse into heavier particles like nitrogen (the more massive the star, the more massive particles it can eventually create).

When looking for these stars, astronomers might mistake them for very dense neutron stars. Their density would ultimately be more dense than theory predicts for a neutron star, which might give them away. In addition, the electroweak stars might not cool down nearly as fast as neutron stars.

Check out other stories on electroweak stars at, the iTwire, and New Scientist.


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