Shielding Against Gamma Ray Bursts

Gamma-ray bursts (GRBs) are the most energetic radiation events observed in the universe. They are characterized as brief but extremely powerful outbursts of gamma rays, which are the highest-energy form of electromagnetic radiation. GRBs can release energy equivalent to that of a billion trillion suns in a matter of seconds, making them the brightest and most extreme explosions since the Big Bang[1][2][4].

Destructive Power, Could A GRB Vaporize the Earth?

Gamma-ray bursts can release an enormous amount of energy, typically in the range of 10⁴⁴J to 10⁴⁷J. Let’s take a gamma-ray burst (GRB) as an example with a total output energy of 10⁴⁵Joules. The energy output of 10⁴⁵ Joules for a gamma-ray burst (GRB) is typically not emitted isotropically (in all directions). Instead, it is highly focused into narrow jets. The output of 10⁴⁵J is the “isotropic equivalent energy” – the energy the burst would have if it emitted equally in all directions, but it doesn’t. The true energy, accounting for beaming, can be 100 or more times smaller.  Since energy decreases with the square of the distance, we can calculate the energy output of this 10⁴⁵J GRB at different distances:

• At 1 light year: 8.41×10¹⁶ J m²
• At 10 light years: 8.41×10¹⁴ J m²
  
• At 100 light years: 8.41×10¹²J m²
  
• At 1,000 light years: 8.41×10¹⁰ J m²
  
• At 10,000 light years: 8.41×10⁸ J m²
  
• At 100,000 light years: 8.41×10⁶ J m²
  

The mass of Earth is approximately 5.97×10²⁴ kg. The energy required to vaporize Earth can be estimated using the concept of latent heat of vaporization and the specific heat capacity of the Earth’s materials. The total energy required to vaporize Earth involves heating it to its boiling point and then providing the latent heat to convert it from a solid/liquid state to a gaseous state. To simplify, we can assume an average temperature increase from the Earth’s average surface temperature (about 300 K) to the boiling point of silicate materials (around 2500 K). From this we can determine the energy it would take to completely vaporize our planet.

• Energy to Vaporize Earth: 1.49×10³¹ J

The distance power values for our GRB of 10⁴⁵Joules represent the energy flux density at each distance, not the total energy received by Earth. To assess the impact on Earth, we need to consider:

1. Earth’s cross-sectional area: Approximately 1.27 × 10¹⁴ m²
2. Total energy received: Multiply the energy per m² by Earth’s cross-sectional area

For example, at 1,000 light years:

Total energy received ≈ (8.41×10¹⁰ J/m²) × (1.27 × 10¹⁴ m²) ≈ 1.07 × 10²⁵ J This is still significantly less than the 1.49 × 10³¹ J required to vaporize Earth, even at relatively close distances.

At a distance of 1 light year, the total energy received by Earth from a GRB would be approximately 1.07×10³¹ J, which is close to the energy required to vaporize Earth (1.49×10³¹ J).

There are no stars (other than our sun) within 1 light-year of Earth. The closest star system to Earth is the Alpha Centauri system, which is approximately 4.37 light-years away, with Proxima Centauri being the closest star at about 4.24 light-years from Earth. Proxima Centauri, the closest star to the Sun, has an approximate mass of 2.428×10²⁹ kg. This red dwarf star is about 12.5% of the Sun’s mass, making it a low-mass star. There is zero possibility of Proxima Centauri ever emitting a GRB.

The Experience of a GRB

As purely a thought experiment, if a gamma-ray burst (GRB) hit Earth while you were outside on a clear day, you would likely observe the following sequence of events:

An incredibly bright flash of light in the sky, brighter than anything you’ve ever seen before[13][16]. This would be due to the Compton scattering of gamma rays in the atmosphere, creating a burst of visible light[13]. The sky would change color dramatically, potentially appearing to glow or taking on unusual hues[13][16]. You would likely experience immediate and severe sunburn-like effects on any exposed skin due to the intense radiation[13][14]. Electronic devices around you would likely fail or malfunction due to the electromagnetic pulse associated with the GRB[16]. The air around you might appear to shimmer or distort as the gamma rays ionize the atmosphere[15]. If you survived the initial blast, you might notice rapid changes in weather patterns or atmospheric conditions in the following minutes to hours[14]. The effects would be catastrophic and likely fatal for most life on Earth’s surface. The gamma rays would quickly deplete the ozone layer, leaving the planet exposed to harmful ultraviolet radiation from the Sun[14]. The ionization of the atmosphere could potentially lead to the formation of nitrogen oxides, which could cause acid rain[14].

However, it’s crucial to understand that such a scenario is extremely unlikely. All GRBs observed to date have occurred far outside our galaxy and pose no threat to Earth[16][17].

In reality, if you were to witness a GRB hitting Earth, you likely wouldn’t have time to observe much before the effects became lethal. The intense radiation would cause severe damage to living organisms almost instantaneously[13][14][16].

Did A GRB Cause any of Earth’s Past Mass Extinctions?

Direct Radiation Damage: At a distance of 200 ly, the direct radiation from a GRB could be intense enough to cause immediate and severe damage to living tissues, potentially leading to mass extinctions. The radiation could also disrupt the DNA of organisms, leading to long-term genetic damage.

Historical Evidence: There is some evidence suggesting that past mass extinction events on Earth may have been caused by nearby GRBs. This historical context supports the idea that a GRB within 200 ly could have devastating effects on life on Earth. Some researchers have suggested that certain mass extinction events, such as the Ordovician-Silurian extinction around 450 million years ago, might coincide with the timing of potential GRB events. This correlation is based on geological and fossil records that indicate sudden and severe environmental changes.

While this hypothesis is intriguing, it remains a topic of ongoing research and debate. There is no direct evidence linking specific mass extinction events to GRBs, but the potential mechanisms and historical correlations make it a plausible scenario worth exploring further.

GRB Effects on Earth, Distance is Everything

Anything within the direct path of a GRB beam, up to a distance of around 200 light years, can be destroyed (if not vaporized) due to the intense energy output. This includes planets, moons, and other celestial bodies. Fortunately, there are no stars within 200 light years of Earth that are likely to produce a GRB in the near future.

If a nearby GRB were to hit Earth directly, it could potentially sterilize half of all life on the planet, even from greater distances within the Milky Way. The radiation could cause severe atmospheric changes, including the breakdown of ozone, allowing more UV radiation to reach the surface, and potentially triggering global cooling.

Earth is actually hit by GRBs almost daily, but these are from sources so distant that their energy has dispersed to harmless levels by the time it reaches us. This information is confirmed by the European Space Agency (ESA). According to ESA, “Earth is bombarded by gamma rays created by cataclysmic explosions in distant galaxies” for a few seconds every day. These explosions, known as gamma-ray bursts, are detected almost daily and are scattered randomly throughout the Universe.[12]

Characteristics of Gamma-Ray Bursts

1. Energy Output: A typical GRB can emit as much energy in a few seconds as the Sun will produce over its entire 10-billion-year lifetime. This immense energy is primarily released in the form of gamma rays, although some bursts also exhibit luminous optical counterparts[1].

2. Duration: GRBs vary in duration, classified into two main categories: short bursts (lasting less than two seconds) and long bursts (lasting two seconds or longer). The energy output and characteristics of these bursts suggest different progenitor systems, such as the collapse of massive stars or the merger of neutron stars[4].

3. Afterglows: Following the initial gamma-ray emission, GRBs produce an afterglow that can be detected across various wavelengths, including X-ray, optical, and radio. This afterglow can persist for hours to years, providing valuable data about the burst and its environment[1][2].

4. Directional Emission: The energy from GRBs is often collimated into narrow jets, making them appear much brighter when directed towards Earth. This focused emission means that most GRBs do not pose a threat to our planet, as the majority of them are not aimed at us[1][4].

Notable Observations

One of the most significant GRBs recorded is GRB 221009A, which was detected in October 2022. This event was noted for being the brightest and most energetic GRB ever observed, affecting Earth’s atmosphere despite being approximately 2 billion light-years away. Its luminosity was so intense that it temporarily disrupted radio communications and left an imprint comparable to a major solar flare on Earth[3][4].

Planned Avoidance

The size of stars required to form a gamma-ray burst (GRB) is known to be very massive, typically starting at 5 to 10 times the mass of the Sun. An average star size able to generate a GRB may be 30 solar masses. Long-duration GRBs, which account for about 70% of detected gamma-ray bursts, are associated with the collapse of massive stars. These progenitor stars have starting masses of at least 5 to 10 solar masses, with some examples being much more massive. For instance, GRB 030329 was traced to the collapse of a star 25 times the mass of the Sun.

Avoiding stars of this size to map out “safe paths” through the universe for human habitation is not a practical or necessary approach: GRBs are extremely rare events. No gamma-ray bursts have been observed from within our own galaxy, the Milky Way. GRBs are highly focused explosions, with most of the energy collimated into narrow jets. The angular width of these jets is typically between 2 and 20 degrees. The chance of a GRB being pointed directly at Earth from a nearby star is extremely low. By the time a civilization would be capable of interstellar travel, they would likely have technologies to detect and potentially shield against such events.

Massive stars are required to form gamma-ray bursts (GRBs). These stars undergo a supernova or hypernova explosion, leading to the formation of a black hole or neutron star, which can result in a GRB if conditions are right. By avoiding regions of space where such massive stars are present or likely to form, it is theoretically possible to map out safer paths through the universe for human habitation.

Based on our current understanding of the stars in our local stellar neighborhood, the number of stars capable of forming gamma-ray bursts (GRBs) within 200 light-years of Earth is indeed extremely low, likely ranging from zero to perhaps a handful at most. This conclusion is supported by several factors:

• GRB progenitor stars are very massive, typically having masses greater than 30 times that of the Sun.
• Such massive stars are rare compared to smaller, more common stars like our Sun.
• Massive stars have short lifespans, quickly exhausting their fuel and ending their lives as supernovae or hypernovae.
• The region within 200 light-years of Earth is a relatively small volume of space in galactic terms.
• Our local stellar neighborhood is not particularly active in terms of star formation, especially for massive stars.

Given these factors, it’s highly unlikely that there are many, if any, stars capable of producing GRBs within 200 light-years of Earth.

Shielding Against Gamma Ray Bursts

There are no anticipated nearby GRBs, but depending on the distance, shielding may make the difference between a human library of knowledge and earth’s genetic material surviving one or not. Shielding against GRBs is challenging due to their immense power, and the fact that they can vary significantly in duration, typically lasting from a few milliseconds to several minutes. Here are some proposed strategies:

1. Atmospheric shielding: Earth’s atmosphere provides some natural protection against cosmic gamma rays. The atmosphere absorbs and scatters a significant portion of incoming gamma radiation, reducing its intensity at ground level.
2. Dense materials: Lead, concrete, and other dense materials can effectively block gamma radiation. However, the thickness required for complete protection from a nearby GRB would be impractical for most applications.
3. Underground shelters: Deep underground structures offer substantial protection from gamma radiation. The earth itself acts as a natural shield, with greater depths providing more protection.
4. Building materials: In the event of a GRB, buildings can provide some shielding. Brick buildings offer better protection than brick veneer structures, which in turn are more effective than frame buildings
5. Electromagnetic field shielding: An innovative approach proposed by researchers involves creating shielding swarms of small objects or particles confined by electromagnetic fields. This concept aims to mitigate the threat from supernovae and gamma-ray bursts to intelligent life.
6. Water shielding: Large bodies of water can attenuate gamma radiation. According to the American Nuclear Society, about 13.8 feet of water would be needed to completely block typical gamma rays
7. Selective shielding: For personal protection in high-risk scenarios, solutions like the StemRad 360 Gamma focus on shielding the most vulnerable parts of the body, particularly bone marrow tissue. This approach provides critical protection without the impracticality of full-body shielding.

Lead as an Example for Thickness Needed

Lead (Pb) is a soft, grayish metal. Each atom contains a nucleus with 82 protons surrounded by a tightly held electron cloud of 82 electrons, giving it the highest atomic number of the non-radioactive elements. Unfortunately, lead is toxic and it accumulates in the body. Repeated exposure results in cumulative poisoning, inducing cognitive deficits and kidney disease. Lead dust is an environmental hazard for humans on earth.

Density of Lead vs Asteroid Material

Lead has a density of approximately 11.34 g/cm³ . In comparison, the most common type of asteroid material, which is often classified as a carbonaceous chondrite, typically has a density ranging from 1.8 to 3.0 g/cm³. This means that lead is significantly denser than the materials that make up most asteroids, being roughly 4 to 6 times denser than these common asteroid materials. This high density is one of the reasons lead is used for radiation shielding, as it effectively absorbs and attenuates gamma rays and other forms of radiation.

One to two meters of lead would provide substantial shielding against gamma radiation, including that from a gamma-ray burst (GRB) and galactic cosmic rays (GCR).

Lead Shielding Effectiveness

1. Gamma Radiation: The halving thickness of lead is about 1 cm, meaning that each additional centimeter reduces gamma radiation intensity by 50%. Therefore, 1 meter (100 cm) of lead would reduce gamma radiation to approximately 1/2¹⁰⁰, which is an extremely low intensity, effectively shielding against most gamma rays, including those from GRBs[7][8].

2. Galactic Cosmic Rays (GCR): GCR consists of high-energy protons and heavier ions, which require thicker shielding than gamma rays. While the exact thickness needed can vary based on the specific energy of the particles, estimates suggest that several meters of dense material, such as lead, would be necessary to provide adequate protection against GCR.

While 1 to 2 meters of lead would be very effective against gamma radiation from GRBs, it may still be insufficient for complete protection against the high-energy particles in GCR, which would require additional shielding or a combination of materials to ensure safety.

Summary

In summary, gamma-ray bursts are the most energetic radiation phenomena known, characterized by their extreme brightness and energy output, making them key subjects of study in astrophysics. A nearby GRB would be an extremely catastrophic event. The best defense against GRBs is the vastness of space itself, which makes such an event in our cosmic neighborhood extremely unlikely. Current scientific understanding suggests that the risk of a dangerously close GRB affecting Earth is very low. A thick walled lead shielded vault as insurance against the unlikely has potential value, but is unlikely to be needed.

More Reading

^{[1] https://en.wikipedia.org/wiki/Gamma-ray_burst
[2] https://science.nasa.gov/universe/gamma-ray-bursts-harvesting-knowledge-from-the-universes-most-powerful-explosions/
[3] https://www.reddit.com/r/spaceporn/comments/1bk5wbz/the_most_energetic_gammaray_burst_ever_recorded/
[4] https://www.space.com/gamma-ray-burst.html
[5] https://en.wikipedia.org/wiki/GRB_080916C
[6] https://www.nrc.gov/docs/ML1122/ML11229A721.pdf
[7] https://www.imagesco.com/geiger/lead-shielding-guide.html
[8] https://www.nuclear-shields.com/radiation-shielding/lead-shielding.html
[9] https://www.arpansa.gov.au/understanding-radiation/what-is-radiation/ionising-radiation/gamma-radiation
[10] https://barriertechnologies.com/lead-thickness-for-radiation-protection/
[11] https://www.epa.gov/radiation/radiation-terms-and-units
[12] https://www.esa.int/Science_Exploration/Space_Science/Space_for_you/Gamma-ray_bursts_are_we_safe
[13] https://www.reddit.com/r/askscience/comments/2g1pxf/what_would_i_observe_if_the_earth_were_hit_by_a/
[14] https://astrobiology.nasa.gov/news/how-deadly-would-a-nearby-gamma-ray-burst-be/
[15] https://www.scientificamerican.com/article/the-brightest-gamma-ray-burst-ever-recorded-rattled-earths-atmosphere/
[16] https://www.space.com/gamma-ray-burst.html
[17] https://en.wikipedia.org/wiki/Gamma-ray_burst}