Death from Space — GRBs

Imagine you could gather the energy form every star within 100,000,000 light years. Imagine you could pack all the energy the Sun will release in its 10,000,000,000 years lifetime and put it inside a cosmic ray gun ready to obliterate anything in its path over a very, very long distance.

What is a GRB?

According to Doyle (Astrobiology Mag.), Gamma-ray bursts (GRBs) are the “brightest electromagnetic blasts known in the Universe”. Most cosmic explosions in the Universe spread out and fade but GRBs are concentrated over a small focus area making them extremely bright and deadly due to its high composition of gamma rays. They are formed by the collapse of the most massive types of stars into a supernova or from the collision of two neutron stars.

Both supernova and neutron star merges make the same thing: black holes surrounded by a magnetized disc of gas left over from their parent stars. “In these environments,” said Kurzgesagt, “the rotation winds up the magnetic field, which funnels hot jets of particles, traveling at nearly the speed of light”.

The gas in this funnel creates two tight jets of high energy gamma rays like a “celestial laser gun”.

Death from GRBs

The universe is full of these cosmic snipers, firing randomly into the dark.

If one such burst were to hit us, we would burn and EveryoneDiesTM (or at least the part that’s facing the GRB). So far, all the GRBs detected are very far away and is not thought to cause us any interference given that, according to Grant, Earth is situated well in the outer suburbs of the Milky Way, 28,000 light years from the center.

GRBs occur far more often in denser regions of stars than the outskirts of the galaxy. If Earth’s distance from the galactic center were halved, “the planet would be sterile”.

But a study reported in the Dec. 5 Physical Review Letters concludes that gamma-ray bursts can be a threat to life on Earth and may have actually contributed to one of the 5 mass extinctions.

A gamma-ray burst doesn’t need to be concentrated or near enough to cause global damage to life. A GRB 4000 light years away, if directed at Earth, would have a hundred-light-years-width by the time it reaches us.

A gamma-ray burst would break up molecules in the atmosphere and nearly destroy the ozone layer. We no longer would have protection from the Sun’s deadly UV rays and EveryoneDiesTM.

There is a very good chance that at least one lethal GRB took place within the last 5 gigayears, and is thought to have caused the Ordovician extinction 450 million years ago when 85 % of all marine species were eradicated.

We May Be Alone After All

Gamma-ray bursts could even be one reason why we don’t see life anywhere else in the universe. They might be wiping out regular chunks of it on a regular basis.

Assuming that a similar level of radiation would be lethal to life on other planets, we will find that a large number of them are located in a location with a high probability of a lethal GRB especially in the inner Milky Way and highest density regions in other galaxies.

When considering the Universe as a whole, according to the study, life can only exist in about 10 % of galaxies.

Of course, this comes with criticisms including from Melott who suggested that “if a planet has a really, really thick atmosphere, or if there’s life under ice, then those types of places would be nearly immune to the effects of a GRB.” He points out examples such as Jupiter’s moon Europa and Saturn’s moon Enceladus (SN: 5/17/14, p. 20) which many scientists suspect that life could thrive in oceans buried under their sheets of ice.

Are We Going To Die?

So, are we going to die from a GRB heading towards us?

Probably not, says Kurzgesagt. In a galaxy like ours, there may only be one GRB per millennia. And to harm us, they must be “close and directed to us”.

But since GRBs travel at the speed of light, we won’t know when it’s headed our way until it arrives.

So, we won’t know if a GRB is headed towards us until it actually hits us, and EveryoneDiesTM.

References

1. Kurzgesagt — In a Nutshell. Death From Space — Gamma-Ray Bursts Explained. YouTube, published July 31, 2016, https://www.youtube.com/watch?v=RLykC1VN7NY&t=329s. Accessed March 19, 2019.
2. Grant, Andrew. Gamma-ray bursts may repeatedly wipe out life. Science News, published December 16, 2014. https://www.sciencenews.org/article/gamma-ray-bursts-may-repeatedly-wipe-out-life. Accessed March 19, 2019.
3. Piran, Tsvi and Jimenez, Raul. “Possible Role of Gamma Ray Bursts on Life Extinction in the Universe.” Gamma-Ray Bursts Determine Potential Locations for Life, Vol. 113, Iss. 23–5 December 2014, https://doi.org/10.1103/PhysRevLett.113.231102. Accessed March 19, 2019.
4. Doyle, Amanda. HOW DEADLY WOULD A NEARBY GAMMA RAY BURST BE? Astrobiology Magazine, published October 10, 2016, doi: https://www.astrobio.net/news-exclusive/deadly-nearby-gamma-ray-burst/. Accessed March 19, 2019.
5. A.L. Melott et al. Did a gamma-ray burst initiate the late Ordovician mass extinction? International Journal of Astrobiology. Vol. 3, January 2004, p. 55. doi: 10.1017/S1473550404001910.