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FAST RADIO BURSTS (Signals from the Cosmos)


Radio Astronomy has now become quite a common field of Astronomy. We can observe the Universe in more larger depths where the optical instruments can't help. Radio telescopes are the key players which not only helped us discover the cosmic rays like gamma rays, X-rays etc but also assured us the presence of a exotic element which we call as Dark Matter. We have leaped a great step over this past years by observing fascinating objects like pulsars, discovering extrasolar planets and most importantly capturing the first ever image of a Black Hole. However, the Universe never leaves us with all the answers to our questions. It also throws googlies onto us which leaves us more freaked out!!

This is where Fast Radio Bursts come into picture. These bursts or pulses are similar to the radio frequencies our radio telescopes observe everyday. The mysterious part is that we have no idea from where these bursts of radio waves originate. Some of these bursts take place and don't appear again while others can give frequent visits to us but are not periodic though. This thing makes us more stunned!!


Theory:

In radio astronomy, a fast radio burst(FRB) is a transient radio pulse of length ranging from a fraction of a millisecond to a few milliseconds, caused by some high-energy astrophysical process not yet understood. While extremely energetic at their source, the strength of the signal reaching Earth has been described as 1,000 times less than from a mobile phone on the Moon. The first FRB was discovered by Duncan Lorimer and his student David Narkevic in 2007 when they were looking through archival pulsar survey data, and it is therefore commonly referred to as the Lorimer Burst.



Fast radio bursts (FRBs) have likely happened for billions of years. But humans only discovered them in 2007, and have detected only a few dozen of them since. And in June 2019, astronomers finally tracked an FRB to its home galaxy. 

But no one knows what causes them. Because these bursts are so rare, unusual and bright — considering that they're visible from billions of light-years across space — physicists have tended to assume they come from a cataclysmic event, such as the collision of stars. No one knows what this pattern means, the researchers noted in a statement, but this pattern doesn't fit neatly into any existing explanations for FRBs.


Capturing these Bursts:

1) known FRB's - 50

2) Estimated Rate - 1000/sky/day

Fast Radio Bursts can be detected over a wide range of frequencies starting from a few hundred MegaHertz to a few GigaHertz.

A single FRB can be observed over a wide frequency band over a period of time. This phenomena is caused due to the dispersion of these radio waves by interstellar medium. Space is not a vacuum! interstellar medium is a space filled with ionized plasma full of charged particles. As light is dispersed by a prism similarly, interstellar medium acts as a prism of radio waves. Hence, waves of different wavelengths have different speeds and reach to us at different time intervals. The degree by which this delay in the signal reception is corrected gives us the distance of these bursts from us. It has come to know that these bursts arrive from cosmological distances.


The Sky Localization Problem:


Given is a diagram of angular resolutions of the radio telescopes primarily used for observing the FRB's. Greater the circle lower is the resolution while smaller the circle higher is the resolution.

Higher resolution gives us a window for focusing nearly exact location from where these bursts arrive. Therefore, the Very Large Array(VLA) was used with an aim to find the source of these bursts.


A total of nine bursts were caught by the VLA in 2016 pointing out their precise sky positions. Now as the location of these bursts were known, scientists pointed the 8.1 meter optical/infrared telescope "Gemini" in the direction of these bursts and found a small smudge of galaxy from which the bursts were coming. This proved that the bursts were coming from cosmological distances.


Theories behind FRB:

1) Exploding star ?

2) Colliding neutron stars ?

3) Evaporating black holes ?

4) Oscillating primordial cosmic strings ?


Where do we stand ?

1) At least one FRB repeats.

2) Rules out exploding or colliding stars from this source.

3) Confirms FRB's indeed are cosmological.


New Frontiers:


The Canadian Hydrogen Intensity Mapping Experiment (CHIME) which was meant to note the hydrogen line emissions from different sources is now used for FRB observations. CHIME has four cylindrical shaped radio collectors with 256 antennas over each collector giving a total of 2048 signals collection by the telescope. The telescope is not mobile but the structure of the telescope makes it unique in its own way. As the sky moves above, the telescope takes observations in strips due to its elongated structure. This increases the probability of finding more FRB's and study them


Open Questions:

1) Do all FRB's repeat ?

2) What is the bursting source ?

3) Why is it in a tiny galaxy ?



Need to find MORE!!!


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