GRB 090423 | Credit: NASA/Swift/Stefan Immler
Gamma Ray Burst
Gamma Ray Burst
Content co-written by:
April 12th, 2017
There exists space phenomena so powerful and catastrophic that they may have restricted the ability for most if not all early galaxies from being able to form life. These events, known as Gamma Ray Bursts, have extremely high amounts of energy, and are likely caused by the largest of stars collapsing in on themselves as their fuel sources run out. These powerful events have a unique feature. As they reach their demise and collapse, the energy from the implosion is released into two narrow cones emitted from the poles of the spinning star. When these narrow cones of energy are pointed in the direction of Earth, we are able to witness and observe these incredible and devastating events.
Facts about Gamma Ray Bursts (GRBs)
- GRBs are the most luminous events in the universe known to humankind.
- These phenomena are very likely related to supernovae, but much more powerful. They may be the result of the largest types of stars collapsing in on themselves when the fuel within them reduces to a point where it is no longer is able to sustain and support the star.
- There are at this time two classified types of GRB: Short and Long. Short GRBs are classified as having a duration of less than two seconds, long GRBs last 2 seconds or more.
- Currently approximately one GRB is detected every day. Detection methods are only able to 'find' or 'see' GRBs whose narrow field of emissions are pointed in the direction of Earth, meaning there are many, many more occurrences of GRB each day.
- There is more energy released in a few short seconds of a GRB than will be released by our Sun in its entire lifetime.
- The highest energy GRB ever detected was captured on April 27, 2013. It had 94 million times the energy of visible light and had a lasted for several hours.
What are Gamma Ray Bursts?
Gamma Ray Bursts (GRBs) are believed to originate from the poles of massive type supernova explosions, but there is much debate in astrophysics as to what actually causes them. Unknown objects or forces may still await discovery that will explain their sources, or their progenitors as they are called in astronomy. GRBs are the most luminous explosions in the known universe. They are quick and brilliant bursts of energy that emanate out into space as two narrow, directed beams of photons. They are erratic and sometimes start with a short burst, followed by a quick larger burst but have no real pattern. The amount of energy released in a fraction of a second from a GRB is said to be greater than the energy our Sun emits in its entire stellar lifespan.
Part of the energy released during a GRB is released as photons of light. These photons
How are Gamma Ray Bursts detected?
Specialized detectors and telescopes onboard satellites use various methods to locate GRBs, and then pass that information onto other systems onboard the satellite or back to Earth.
The first Gamma Ray Burst was detected in 1967, when a satellite that was designed to monitor nuclear activity detected non-nuclear gamma ray emissions. However, it wasn't until 1969 when two scientists named Ray Klebesadel and Roy Olsen were looking over data from the mission that the 1967 event was found and speculated to be of cosmic origin. In 1972, along with a third scientist named Ian Strong and using additional information from other satellites, the scientists were able to definitively say that the activity had cosmic origins.
With this new discovery NASA was able to focus in on these events, and eventually they launched a mission designed primarily to learn more about them.
The Swift Gamma-Ray Burst Mission
A satellite was launched in 2004 for the Swift Gamma-Ray Burst mission, and its primary function is the detection of GRBs and sending that data back to Earth. Onboard the satellite are specialized instruments with detectors, each with its own unique function that allow the satellite to accomplish this mission. The following information regarding the Swift Telescope is provided by NASA.
The main instrument, called the Burst Alert Telescope or BAT, has a detector that is made of Cadmium, Zinc, and Tellurium. Its primary function is detecting bursts rapidly and calculating their position, and then sending that information back to the spacecraft and back to instruments on Earth. It detects energies from 15keV all the way up to 500keV, covering the hard X-ray portion of the Electromagnetic Spectrum and a significant portion of the Gamma ray portion.
Current technology detects one GRB a day on average. Interestingly, the bursts are distributed evenly throughout the universe from Earth's perspective. GRBs are difficult to determine in distance and source. They can occur close by in our own galaxy on rare occurrences. They occur at many distances, some billion of light years away therefore explosions whose light has reached our sight from an age long ago. Gamma Ray Burst (GRB 090429B) detected in 2009, is currently the most distant object identified in the universe. It is estimated to have originated from approximately 13 billion light years away nearly the age of the universe! These distant GRBs are a glimpse back in time and far away.
Types of Gamma Ray Bursts
GRBs are typically defined as either 'long' or 'short'.
The most common GRBs are known as long-duration gamma ray bursts and are hypothesized to originate from superluminous supernova known as hypernova; a stellar explosion that is 10x or even 100x more luminous than a typical supernova. This occurs when a massive low-metallicity star collapses its core, thought to form a black hole, sending out pulses of gamma-rays into space. A 'long' GRB lasts between 2 seconds to over a minute. The first confirmed superluminous supernova that emitted gamma-rays was observed only in 2003. It is now speculated that stars 40x in mass or greater than our Sun are candidates for superluminous supernova.
Short-duration gamma ray bursts have durations from microseconds up to 2 seconds and are thought to originate from binary systems collapsing and coalescing onto each other. These systems may be made up of some combination of neutron stars and black holes. They are not associated with massive supernova collapse as are the long-duration GRBs. There is much unknown about the nature and origin of GRBs. In the future the classification of GRBs will undoubtably change as technology evolves and new discoveries are made.
Are Gamma Rays a threat to Earth?
A team of scientists at Ohio State University concluded there is basically zero risk. Krzysztof Stanek and colleagues say that GRBs originate from within small metal-poor galaxies. The Milky Way is a large spiral galaxy containing a lot of heavy metals not conducive to GRBs.