Gamma Ray Bursts Form Jets Moving Faster than Light (in Clouds)

The Cosmic Companion
Sep 25 · 4 min read

Cosmic ray bursts produce the most-powerful blasts witnessed since the big bang. New research shows jets formed by these events could travel faster than their local speed of light.

Blasts responsible for gamma ray bursts (GRB’s) could travel through their local gas clouds faster than the local speed of light, a new study suggests. However, this bizarre-sounding idea does not violate the universal speed limit of the Universe.

Albert Einstein was the first person to recognize that no object could travel through space faster than the speed of light in a vacuum. However, these jets would not violate this universal speed limit, as the speed of light in mediums (such as gas clouds) is lower than its speed in a vacuum.

The local speed of light in the clouds at the center of this study is uncertain. This value also changes over time, depending on the acceleration of the blast wave as it passes.

An artist’s concept of a jet erupting from the region of a black hole, at the center of a blazar, a highly-active galaxy emitting a jet of matter at nearly the speed of light, toward the direction of Earth. Image credit: DESY, Science Communication Lab (used with permission by Astronomy Picture of the Day, which is co-managed by Robert Nemiroff at Michigan Tech).

It All Started with a Big Bang (Not That One)

Gamma ray bursts are short-lived blasts of gamma ray radiation, the most energetic of all forms of electromagnetic radiation. Lasting between a few thousands of a second to several minutes, these events can release a million trillion times as much energy as our Sun. These GRB’s are hundreds of times more powerful than typical supernovas, and often result in the creation of new black holes.

“Gamma-ray bursts (GRBs) can be created when stars die violently. GRBs are among the most powerful explosions we know of in the universe and related to specific types of supernovas. Because gamma-rays are beamed and can go through almost anything, we see GRBs further out into the universe than any other type of explosion,” Dr. Robert Nemiroff of Michigan Technological University tells The Cosmic Companion.

These events were first discovered in the 1960’s by U.S. military satellites searching for gamma rays emitted during nuclear weapons testing.

There are two recognized classes of GRB’s, long- and short-duration, where long-duration events typically last between two seconds and a few minutes. They are thought to be associated with the explosive deaths of massive stars as supernovae, although not all such stellar deaths emit GRB’s.

“Short duration bursts are those that last less then 2 seconds; lasting anywhere from a few milliseconds to 2 seconds with an average duration of about 0.3 seconds (or 300 milliseconds). These bursts appear to be associated with the merger of two neutron stars into a new black hole or a neutron star with a black hole to form a larger black hole,” NASA explains.

An artist’s impression showing jets of a GRB striking surrounding debris, in a process known as reverse shock. Image credit: NRAO/AUI/NSF, S. Dagnello

These high-energy events can come about from several scenarios playing out between large masses, like dense stellar corpses.

“Gamma-ray bursts (GRBs) can also be created when neutron stars in binary systems coalesce. So our model applies to both merging neutron stars and beamed supernovae,” Jon Hakkila of The College of Charleston and first author of the paper announcing this finding, explains to The Cosmic Companion.

One unusual form of these events are dark gamma ray bursts, which bathe their surrounding area with gamma rays and X-rays, while remaining nearly invisible in visible light.

Dense knots of dust dim visible light from a dark GRB, while X-rays and gamma rays pass through the barrier. Image credit: NASA/Swift/Aurore Simonnet

“Explosions are not comfortable.” — Yevgeny Zamyatin

Radiation is released as the expanding jet from a GRB passes through the gas cloud at superluminal speeds.

“The impactor wave interacts with the surrounding medium to produce Cerenkov and/or other collisional radiation when traveling faster than the speed of light in this medium,” researchers describe in The Astrophysical Journal.

Prior to this study, Cerenkov radiation was not thought to contribute significant amounts of energy to gamma ray bursts.

Cherenkov radiation photographed at the Reeed Research Reactor in Oregon, USA. Public domain image.

Waterfront Property, Perfect for Physics

The superluminal (faster-than-light) phenomenon are thought to create conditions called time-reversible light curves, where events are seen in the opposite order from which they are created.

One way of picturing this phenomenon is by imagining yourself standing near a pond, with another person on the opposite shore. If that person were to skip a rock toward you, ripples would form each time the rock touched the water, and travel outward in circles.

However, the rock itself would fly through the air toward your observation point at a speed greater than the velocity at which the ripples travel across the water. From your standpoint, you would see the final wavelet hit your shore before the initial ripple caused when the rock first touched the water. As time progressed, the wavelets would strike your shore in the reverse order from which they were created.

Similar structures created in the regions surrounding GRB’s are seen in the form of superluminal jets.

“Standard gamma-ray burst models have neglected time-reversible light curve properties. Superluminal jet motion accounts for these properties while retaining a great many standard model features,” Jon Hakkila of the College of Charleston explains.

Lessons learned from this study could be applied to the study of all classes of GRB’s, researchers suggest, pointing the way to new discoveries.

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The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

The Cosmic Companion

Written by

James Maynard is the author of two books, and thousands of articles about space and science. E-mail:

The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

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