Recent Gamma Ray Bursts

Long before experiments could detect gamma-rays emitted by cosmic sources, scientists had known that the Universe should be producing such high energy photons. Hard work by several brilliant scientists had shown us that a number of different processes which were occurring in the Universe would result in gamma-ray emission. These processes included cosmic ray interactions with interstellar gas, supernova explosions, and interactions of energetic electrons with magnetic fields. In the 1960s, we finally developed the ability to actually detect these emissions and we have been looking at them ever since!

Gamma-rays coming from space are mostly absorbed by the Earth's atmosphere. So gamma-ray astronomy could not develop until it was possible to get our detectors above all or most of the atmosphere, using balloons or spacecraft. The first gamma-ray telescope carried into orbit, on the Explorer XI satellite in 1961, picked up fewer than 100 cosmic gamma-ray photons. These appeared to come from all directions in the Universe, implying some sort of uniform "gamma-ray background". Such a background would be expected from the interaction of cosmic rays (very energetic charged particles in space) with gas found between the stars.

Additional gamma-ray experiments flew on the OGO, OSO, Vela, and Russian Cosmos series of satellites. However, the first satellite designed as a "dedicated" gamma-ray mission was the second Small Astronomy Satellite (SAS-2) in 1972. It lasted only seven months due to an electrical problem, but provided an exciting view into the high-energy Universe (sometimes called the 'violent' Universe, because the kinds of events in space that produce gamma-rays tend to be explosions, high-speed collisions, and such!). In 1975, the European Space Agency launched a similar satellite, COS-B, which operated until 1982. These two satellites, SAS-2 and COS-B, confirmed the earlier findings of the gamma-ray background, and also detected a number of point sources. However, the poor resolution of the instruments made it impossible to identify most of these point sources with individual stars or stellar systems.

So what are gamma-rays and what can they tell us about the cosmos? Gamma-rays are the most energetic form of electromagnetic radiation, with over 10,000 times more energy than visible light photons. If you could see gamma-rays, the night sky would look strange and unfamiliar. The familiar sights of constantly shining stars and galaxies would be replaced by something ever-changing. Your gamma-ray vision would peer into the hearts of solar flares, supernovae, neutron stars, black holes, and active galaxies. Gamma-ray astronomy presents unique opportunities to explore these exotic objects. By exploring the universe at these high energies, scientists can search for new physics, testing theories and performing experiments which are not possible in earth-bound laboratories.

Sometimes astronomers plan for years to make a crucial scientific discovery, building a telescope to precise specifications, launching it into space, and conducting a series of long, careful surveys of stars and galaxies.
And sometimes they just get lucky.

For a gamma-ray burst that occurred on December 6, 2002, it was a little of both.
Gamma-ray bursts are the most powerful explosions known in the universe, likely culminating in the creation of a black hole, yet their origins still remain a mystery. During a chance observation, NASA's RHESSI satellite made one of the most important discoveries about these bursts in the past decade.

The satellite, called the Reuven Ramaty High-Energy Solar Spectroscopic Imager in full, detected for the first time that the light from these distant bursts can be polarized. This was big news to scientists, because it speaks of the underlying mechanics of the explosion.

Polarized light, familiar to most of us as the reflected glare blocked by Polaroid sunglasses, is light with its magnetic and electric fields vibrating primarily in one direction. Usually the light waves hitting our eyes are vibrating randomly in all directions. The December gamma-ray burst was about 80 percent polarized. That's a lot. Theorists had expected only 2 to 3 percent polarization. Some great force must have been present to polarize the light.

Gamma-ray bursts must originate from a region of highly structured magnetic fields, stronger than the fields at the surface of a neutron star -- until now, the strongest magnetic fields observed in the universe.
In the meantime, astronomers and scientists keeping there fingers crossed, hoping to get lucky.

~Maiya Wenzel

Black Holes

Black holes are the endpoint of the life of super-massive stars.

If a star ten or more times the size of our Sun undergoes a supernova explosion, it can leave behind a burned out stellar remnant (matter left over from the original star). With no force but its own gravity acting on it, the remnants will collapse in on itself. The remnants eventually collapse to the point where it has zero volume and infinite density creating "singularity ". As the density increases, light rays emitted from the now collapsed star remnants are bent and wrapped around a center point. When this happens, the gravitational force creates an intense gravitational field. A black hole has been created.

The huge gravitational pull of a black hole pulls in anything that crosses inside its Schwarzschild Radius. Nothing can escape- not even light itself. At the Schwarzschild Radius, the escape speed is equal to the speed of light. The Radius traps everything from stars to single protons.

* The Schwarzschild radius can be calculated using the following equation for escape speed: Vesc = (2GM/R)1/2 For photons, or objects with no mass, we can substitute c (the speed of light) for Vesc and find the Schwarzschild Radius, R, to be: R = 2GM/c2

Let’s say the Sun is replaced with a black hole with the same mass. The Schwarzschild Radius would be 3 km, compared to the Sun's radius of nearly 700,000 km. The Earth would have to get very close to be sucked into the black hole.

Identifying Black Holes

Since black holes can be rather small, and the light they have can’t escape, a black hole alone would be hard to see. We can see black holes, though, when they pass through a cloud of interstellar matter or get close to a star becuase matter from the star is sucked in. As matter is sucked into the black hole it gains kinetic energy and heats up. When the matter reach a few million Kelvin it emits X-rays. The rays escape the pull before the matter reaches the Schwarzschild radius, and we in turn can see it.

Another sign of a black hole is a random variation of emitted X-rays. Matter that emits X-rays does not fall into the black hole at a steady rate. Instead, it releases the rays sporadically, which causes a variation in the intensity of the X-rays.

~Sophia Thomson

Wormholes

Beyond the dangers of spaghettification and collisions with singularities, the tunnel that connects a black hole to another universe stays open only briefly and then collapses. But there may be an alternative, although at the moment it exists only in theory. One day, scientists may be able to turn off the fury of a black hole using antigravity- the opposite of gravity- to create a wormhole. A wormhole has two mouths that are connected by a tunnel through curved space. Unlike the event horizon of a black hole, the mouth of a wormhole allows two-way traffic: you can enter and leave. And a wormhole also has the great advantage that it can connect different parts of our own Universe, providing a safe shortcut between two distant places.

A wormhole’s mouth would look like the entrance to a non-spinning black hole. The difference is that there is no event horizon, so traffic can cross in both directions in and out of the tunnel.

The image of the other end of the wormhole is distorted because the light rays follow the flared mouth of the wormhole, which bends them like a lens.

-Maiya Wenzel