Blazars: Deadliest objects in the Universe?

Understanding dangerous black hole variants in space  - Blazars

It's almost unbelievable that the term 'blazar' is not fancied enough by the scientific community when compared to its cousins - quasars, pulsars and magnetars! 

Of course, quasars and pulsars are getting all the attention they deserve because we've actually got a chance to observe them through radiation and signals that we receive from space telescopes. So, it's really not our fault if we claim that we know more about quasars or pulsars better than blazars. In fact, blazars are one of the rarest events in the universe that is to be observed by us, directly or indirectly. It is also termed as one of the most energetic and deadliest space events in the universe, so maybe it's a good thing that they're rare after all!

But what exactly are blazars? We do know that they belong to the family clan of black holes and neutron stars - quasars, pulsars and magnetars. We also know that they are awfully bright and energetic active galaxies, similar to quasars. If so, what is it that makes blazars stand out from other active black hole variants?

What are blazars?

Blazars are the name given to active supermassive black holes that are located at the centre of a galaxy. 

Image by NASA - Simulation of the M87 galaxy and its central black hole

Blazars can also be classified under the category of Active Galactic Nuclei (AGN). An AGN is the centre of a massive galaxy that is the most luminous and densest region of the galaxy. 

Usually, AGNs are caused when an active supermassive black hole at the heart of a galaxy starts pulling in the matter (matter from nearby stars and planets). This 'swallowing' of matter by the black hole causes the formation of an accretion disk of matter around it, which is accelerated to very high velocities by the gravitational pull of the black hole. Because of this 'soup' of high-velocity particles present in the accretion disk, powerful jets of radiation are given off from the centre of the host galaxy. This very powerful cosmic event is what we call a blazar. 

But here's the deal: we already know that the above phenomenon can also be termed as a quasar since quasars are also identified as a type of AGN caused by an active supermassive black hole. So, does this imply that quasars and blazars are, after all, the same thing? 

Difference between quasars and blazars

Technically, a quasar and a blazar are the same thing - an active black hole that emits jets of radiation from its center! 

Then what is the purpose of this post you ask? It's just that although quasars and blazars are the same things, they're considered as different space events and named differently based on their angle of observation concerning the earth.

In simple terms, quasars are a type of AGN that is pointed away from the earth, which means that its radiation jets (arising from the centre of the host black hole) are not directed towards the earth. This also means that the radiation beams that emerge from the focal point of the accretion disk (of the black hole) are arriving at an angle to our line of sight. 

But in the case of blazars, unlike quasars, their radiation jet beams are pointed directly towards the earth! This means that the angle between our line of sight (from the earth) and the incoming radiation beam is zero.

Basic demonstration of how a quasar appears to an observer on earth

Basic demonstration of how a blazar appears to an observer on earth

To sum up, an Active Galactic Nuclei that's not pointed to our earth is what we call a quasar, and an Active Galactic Nuclei that is pointed to our earth is called a blazar. They're basically the same events, and they're just named differently based on how we view it from the earth.

We already saw that blazars are active supermassive black holes that spew out high-energy radiation toward the earth. This kind of high-energy radiation jet constitutes all kinds of electromagnetic radiation, including powerful gamma rays. This gamma-ray burst from a blazar is so energetic that the radiation is spewed out in a narrow intense jet stream without any dispersion of radiation rays to other directions. Moreover, this single streamed radiation from the blazar would seem much brighter and more energetic than its original luminosity, due to an effect called Doppler Boosting.

How dangerous are blazars?

Imagine a space laser beam that possesses the energy of approx. 10^44 Joules. That is the energy of a blazar jet beam, travelling at nearly the speed of light, approaching the earth!

To have an idea of the lethal energy that it possesses, the energy magnitude of 10^44 Joules is the total energy output produced by the sun in its entire lifetime! If so, a deadly jet stream that powerful, travelling at nearly light speed, can literally melt our earth in just a matter of seconds. If we are to ever encounter a blazar in real life, it's capable of destroying not only our planet but our entire solar system. 

But that is an extremely rare event to occur. Considering our chances of an encounter with lethal blazar radiation, it's not even a possibility for the next few million years. 

The nearest blazar that we've detected from the earth is Markarian 421, and it's about 400 million light-years away from us! Blazars at such distances aren't claimed as 'dangerous' just because it'd take its radiation about 400 million years to reach us, even at the speed of light. 

And as for its energetic gamma radiation, high energy radiation can't travel long for huge distances, since it'll collide with other sorts of radiation that's being given off by stars and other objects. This collision of gamma rays with the background light will result in an electron and positron. So, before we know it, we won't be left with any gamma rays to detect in the first place. 

But in rare cases, we still manage to detect such gamma-ray sources as blazars and quasars using powerful space telescopes. From the resultant positron and electron or even neutrinos, we can trace their paths to their sources. 

Although we aren't in for a risky blazar intervention on earth any time soon, there's something else that remains as lethal and dangerous to our survival - climate change. So, just a reminder that while looking out into our universe for potential disasters and threats, don't ignore the ones that are literally at our doorsteps - and it will be too late for us to act when the time comes, for us and the coming generations! 

To check my post on Quasars for more on the topic, CLICK HERE

To check my post on Magnetars for more on the topic, CLICK HERE