15亿光年外的神秘快速射电暴 | Nature Podcast 学术资讯

我们会在每周日推送 Nature Podcast。欢迎收听本周由 Benjamin Thompson 和 Noah Baker 带来的一周科学故事，本期播客片段讨论加拿大科学家发现的快速射电暴。欢迎前往iTunes或你喜欢的其他播客平台下载完整版，随时随地收听一周科研新鲜事。

音频文本：

Interviewer: Benjamin Thompson

Listeners, I’d like to start 2019 with a bit of a mystery that’s had astronomers scratching their heads for quite some time. This mystery centres on cosmic phenomena known as fast radio bursts, which we’ve covered on the podcast before. Now, their name might give you a small clue as to what they are, but here’s Shriharsh Tendulkar from McGill University in Canada with a bit more detail.

Interviewee: Shriharsh Tendulkar

So, fast radio bursts are these bright flashes of radio waves, in some sense, radio light. If you had eyes which are sensitive to radio light, you’d see these flashes in the sky, and they last only for a thousandth of a second. And they seem to be coming from halfway across the universe.

Interviewer: Benjamin Thompson

Understandably, super brief radio bursts that last for a fraction of a second are easy to miss. To date, just a few dozen have been spotted.

Interviewee: Shriharsh Tendulkar

The first one reported was in 2007 by Duncan Lorimer. Before this we did see flashes of radio light from these objects called pulsars, which are rotating neutron stars, except all these pulsars are in our galactic neighbourhood – they are very nearby and they don’t emit too much energy. And we didn’t expect to see anything from outside the galaxy, so we never looked for it. And now we know that they exist, these bursts which are a trillion times brighter intrinsically than the pulsars that we know of.

Interviewer: Benjamin Thompson

Part of the difficulty with spotting these fast radio bursts is that many telescopes in use focus on a fairly narrow part of the sky. Shriharsh and his colleagues have been using a special telescope in Canada, designed to have a wider view. It’s named is CHIME, and to the untrained eye, it looks like a series of skateboard half pipes laid out next to each other.

Interviewee: Shriharsh Tendulkar

CHIME stands for the Canadian Hydrogen Intensity Mapping Experiment. It is a new telescope built out in British Columbia and CHIME is built for mapping the sky. So, it looks at a huge swab of the sky at any given point of time, and it is a transit telescope, so it doesn’t point to any particular location in the sky. It just looks overhead and as the sky rotates, it makes a map of the sky.

Interviewer: Benjamin Thompson

Last summer, Shriharsh and his colleagues used CHIME to detect 13 new fast radio bursts. Among the new finds, one in particular rather stood out.

Interviewee: Shriharsh Tendulkar

One is a repeater – it’s only the second repeating fast radio burst that has been discovered yet. So most fast radio bursts seem to be single flashes of light. You look at it in the same location with a telescope for a long period of time afterwards and people have not seen anything. People have looked for hundreds of hours. Having a repeating fast radio burst is really special because you can follow it up later. You can look at it with other telescopes, localise it very precisely, and then try to understand it better.

Interviewer: Benjamin Thompson

The only other repeating fast radio burst was discovered in 2016, and this new find shows that it’s not alone. Also striking about the new finds is their radio frequency. Up until now, none have been found below 700 megahertz. In this new work, Shriharsh and his colleagues have found fast radio bursts down to 400 megahertz – the lowest they detect with CHIME – and in a frequency range where none have been seen before.

Interviewee: Shriharsh Tendulkar

Having these detections at 400 megahertz tells us that they do exist – FRBs – and it allows us to study in greater detail what sort of mechanism is causing fast radio bursts to be not detected at low frequencies.

Interviewer: Benjamin Thompson

While this work expands the frequency range in which fast radio bursts have been detected, it still doesn’t tell us where these mysterious intergalactic signals are coming from.

Interviewee: Shriharsh Tendulkar

There are a lot of different theories of what can cause fast radio bursts. There are some theories which involve newly born highly magnetised neutron stars called magnetars, and all these are expected to be in locations of the galaxy where there’d be a lot of activity going on, supernovae and so on and so forth. And then there are other models which could suggest that there are compact neutron star mergers which are happening which would be further outside from the galaxy, and possibly in a cleaner environment.

Interviewer: Benjamin Thompson

Shriharsh reckons that these new fast radio bursts may be coming from what he calls ‘dense and turbulent’ regions of galaxies which contain a large amount of interstellar gas, but this remains to be seen. Understandably, pinning down exactly where fast radio bursts are coming from is something that researchers are very keen to do. Shriharsh is hopeful that the CHIME telescope will help identify many more of these signals, and that these will help us develop a more accurate understanding of our universe.

Interviewee: Shriharsh Tendulkar

As a fast radio burst travels through the universe, it is interacting with electrons and the magnetic field in the universe. There are a lot of different effects which we can study along the line of sight, so when we detect say 10,000 fast radio bursts, we can use this to sort of do a tomography of the universe. We can look through different lines of sight and understand the distribution of matter and magnetic fields in the universe.

Interviewer: Benjamin Thompson

That was Shriharsh Tendulkar. To read his paper head over to nature.com/nature, where you’ll also find a companion paper discussing the repeating fast radio bursts in more detail.ⓝ

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