Fermi telescope: Gamma-ray bursts' highest power side unveiled

Detectable for only a few seconds but possessing enormous energy, gamma-ray bursts are difficult to capture because their energy does not penetrate the Earth's atmosphere.

Now, thanks to an orbiting telescope, astrophysicists are filling in the unknowns surrounding these bursts and uncovering new questions.

The Fermi Gamma-Ray Space Telescope, formerly called the Gamma-Ray Large Area Space Telescope, launched on June 11, 2008. As part of its mission, the telescope records any gamma-ray bursts within its viewing area.

"Fermi is lucky to measure the highest energy portion of the gamma-ray burst emission, which last for hundreds to thousands of seconds -- maybe 20 minutes," said Péter Mészáros, Eberly Chair Professor of Astronomy and Astrophysics and Physics, Penn State.

Most gamma-ray bursts occur when stars that are more than 25 times larger than our sun come to the end of their lives. When the internal nuclear reaction in these stars ends, the star collapses in on itself and forms a black hole. The outer envelope of the star is ejected forming a supernova.

"The black hole is rotating rapidly and as it is swallowing the matter from the star, the rotation ejects a jet of material through the supernova envelope," said Mészáros.

This jet causes the gamma-ray burst, which briefly becomes the brightest thing in the sky. However, unlike supernovas that radiate in all directions, gamma-ray bursts radiate in a very narrow area, and Fermi sees only jets ejecting in its direction.

This, however, is the direction in which they send their highest energy photons. Any gamma-ray bursts on the other side of the black hole or even off at an angle are invisible to the telescope.

"We actually miss about 500 gamma-ray bursts for every one we detect," Mészáros told attendees today at the annual meeting of the American Association for the Advancement of Science in Vancouver, British Columbia.

The gamma-ray bursts that Fermi has seen have allowed astrophysicists to clarify previous theories about gamma-ray bursts.

"We have been able to rule out the simplest version of theories which combine quantum mechanics with gravity, although others remain to be tested," said Mészáros.

Mészáros notes that Fermi and other programs like the SWIFT telescope have shown that gamma-ray bursts last longer than we thought they did and that there are long and short gamma-ray bursts.

Read more about the SWIFT Telescope discovery here

Aliens and Interstellar Archaeology on the Kardashev Galactic Scale

Kardashev Type III and Its Traces
What would happen if a true galaxy-spanning civilisation went to work on astro-engineering?

We call this a Kardashev Type III civilisation, one that could exploit the power resources of an entire galaxy, and the assumption made has always been that such a culture would be very high profile, if not, blindingly obvious. It's projects would be so vast that our astronomers would be able to detect them by noting anomalies, outside of natural occurences.

Imagine, for example, a galactic culture that encloses each individual star in a Dyson sphere.

Image: M81, a spiral galaxy in Ursa Major. A ‘wavefront’ Dyson sphere culture might spread across such a galaxy, causing stars to drop out of visible light spectrum entirely, and then one by one, to be detected in the infrared. Credit and copyright: Giovanni Benintende.

A Dyson sphere or ‘shell’ would absorb all of the visible light from a star, re-radiating stellar energy at infrared wavelengths. A Dyson ‘ring’ would use planetary materials that would mask only part of the star’s light.

Scientists have used a list of very interesting infrared sources from the Infrared Astronomy Satellite (IRAS) in their searches, but have come up with no strong Dyson sphere candidates. Nonetheless, Dyson spheres remain interesting, if only because they vastly increase the habitable area around a star.

What would a Type III civilisation do with technologies that could create Dyson spheres not only in one place but across the galaxy?

Whatever the answer, you would think it would be clearly noticeable. Freeman Dyson himself has said that “…a type III (Kardashev civilisation) in our own galaxy would change the appearance of the sky so drastically that it could hardly have escaped our attention.”

James Annis, who has studied anomalous galaxies in a quest for signs of a Type III civilisation, reports: “It is quite clear that the Galaxy itself has not transformed into a type III civilisation based on starlight, nor have M31 or M33, our two large neighbours.” Nonetheless, we wonder whether we should take these statements as conclusive or definitive:

…what would happen for a civilisation that was on its way to becoming a type III civilisation, i.e. a type II.5 civilisation that is developing?

If it was busily turning stars into Dyson spheres the civilisation could create a “Fermi bubble” or void in the visible light from a patch of the galaxy with a corresponding upturn in the emission of infrared light.

This bubble would grow following the lines of a suggestion attributed to Fermi… that patient space travellers moving at 1/1000 to 1/100 of the speed of light could span a galaxy in one to ten million years.

To read more on Interstellar Archaeology ......