Should You Be Worried about Gamma-ray Bursts?

artist's concept of gamma-ray burster
Artist's illustration of a bright gamma-ray burst occurring in a star-forming region. Energy from the explosion is beamed into two narrow, oppositely directed jets. NASA

There are many cosmic threats to our planet, but one of the weirdest are the gamma-ray bursts (GRBs). These powerful events release huge amounts of gamma rays, which are among the most deadly radiation known. If you were close to one, you'd be fried. That's the bad news.

The good news is that Earth being blasted by a GRB is pretty unlikely. That's because these bursts occur so far away that the chances of being harmed by one are quite small.

Still, they are fascinating events that grab the attention of astronomers whenever they occur. 

Gamma-ray bursts are giant explosions in distant galaxies that send out swarms of powerfully energetic gamma rays. Stars, supernovae and other objects in space radiate away their energy in various forms of light, including visible light, x-rays, gamma-rays, radio waves and neutrinos, to name a few. Gamma-ray bursts focus their energy onto a specific wavelength of particle. As a result, they are some of the most powerful events in the universe, and the explosions that create them are quite bright in visible light, too.

The Anatomy of a Gamma-ray Burst

When two highly magnetized objects, like black holes or neutron stars collide, their magnetic fields join together. That action forms extensive jets that focus energetic particles and photons streaming out from the collision. Those jets extend across many light-years of space.

Think of them like Star Trek-like phaser bursts, only a lot more powerful and reaching out on an almost cosmic scale. 

The energy of a gamma-ray burst that created due to the collapse of a supermassive star (which creates "long-duration bursts"), or the collision of two black holes or neutron stars (associated with short-duration bursts), is focused along a narrow beam (astronomers say it is "collimated").

However short-duration bursts may be less collimated or, in some cases, not highly focused at all.)

Why We See GRBs 

Collimating the energy of the blast means that a lot of it gets focused into a narrow beam. If we happen to be along the line of sight of the focused blast, we detect the GRB right away. It actually produces a bright blast of visible light, too.  A long-duration GRB (which lasts more than two seconds) can produce (and focus) the same amount of energy that would be created if 0.05% of the Sun were instantaneously turned into energy. Now, that's a huge blast!

Understanding the immensity of that kind of energy is difficult. But, when that much energy is beamed directly at us from halfway across the universe, it can be visible to the naked eye here on Earth. Luckily, most GRBs are not that close to us.

How Often do Gamma-ray Bursts Occur?

In general we detect about one burst a day. However, we only detect those which beam their radiation beamed in the general direction of Earth. So, we are likely only seeing a percentage of the total numbers of GRBs that occur in the universe.

Understanding the distribution of gamma-ray bursts is difficult, since they heavily rely on the density of star-forming regions, as well as the age of the galaxy involved (and perhaps other factors as well).

While most seem to occur in distant galaxies, they could happen in nearby galaxies, or even in our own. That seems to be fairly rare, however.

Could A Gamma-ray Burst Effect Life on Earth?

Current estimates are that a gamma-ray burst will happen in our galaxy, or in a nearby galaxy, about once every five million years. However, it's pretty likely that the radiation would not have an impact on Earth. It has to happen pretty close to us for it to have an effect.

It all depends on the beaming. Even objects very close to a gamma-ray burst can be unaffected if they're not in the beam path. However, if an object is in the path, the results can be devastating.

There is evidence that suggests that a somewhat nearby GRB could have occurred about 450 million years ago, which could have led to a mass extinction.

But the evidence for this is still sketchy.

A gamma-ray burst, beamed directly at Earth is pretty unlikely. However, if one did, the amount of damage would depend on how close the burst is. Let's assume that one occurred in the Milky Way galaxy, but very far away from our solar system.

With the gamma-rays beamed directly at us, the radiation would destropy a significant portion of our atmosphere, specifically the ozone layer. The photons streaming from the burst would cause chemical reactions leading to photochemical smog. This would further deplete our protection from cosmic rays. Then there are the lethal doses of radiation that surface life would be experience. The end result would be mass extinctions of most species of life on our planet.

Luckily, the statistical probability of such an event is low. We seem to be in a region of the galaxy where supermassive stars are rare, and binary compact object systems aren't dangerously close. Even if a GRB happened in our galaxy, the likelihood that it would be aimed right at us is even more unlikely.

So, while GRBs are some of the most powerful events in the universe, with the power to devastate life on any planets in its path, we are generally very safe.

 

Edited and updated by Carolyn Collins Petersen.