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Cosmic retrospective — gamma ray bursts

One of the main themes of this blog is “What’s changed in the last 50 years?” — as far as our understanding of physics and the cosmos. For this post, let’s consider the last 100 years or so. There have been major changes in our cosmic perspective. Rather than adding the content of this post as a comment for a previous one on the topic (see notes), I decided that this video visualization merits its own post.

This retrospective on the SpaceRip YouTube channel contains wonderful visuals. Many comments praise the narration. The video takes us from the days of an island universe into the quest to understand distant incredibly powerful gamma ray bursts. In particular, the role that the Swift Gamma-Ray Burst space telescope (now called the Neil Gehrels Swift Observatory) has played in that understanding.

SpaceRip – Premiered Jun 5, 2019 [25 minutes]
This SpaceRip classic explores one of the greatest mysteries in modern science: a series of brief but extremely bright flashes of ultra-high energy light coming from somewhere out in space. These gamma ray bursts were first spotted by spy satellites in the 1960s. It took three decades and a revolution in high-energy astronomy for scientists to figure out what they were: black holes at the moment of their birth.

There have been times when our understanding of the universe has reached a standstill — when our grasp of the workings of time and space, the nature of matter and energy do not fully square with what we observe. In those times, opposing world views cannot be resolved. So it was in the spring of 1920 when astronomers debated the scale of the universe

September 13th 2008, the Swift satellite recorded a burst with the power of 9000 supernovae and a jet that was clocked at 99.9999% the speed of light.

April 29th 2009, brought the second most distant object ever recorded. The journey of this gamma-ray burst started 13.14 billion years ago.

Astronomers have begun to see these beacons as probes for understanding the chemical evolution of the cosmos going all the way back to when stars and galaxies were just beginning to form. But how does nature produce a beacon of light that can reach across the entire breadth of the visible universe? One team of scientists has been looking for answers close to home in a giant galaxy some 50 million light years away known as M87.

Other posts

Photographing a black hole?
Cosmological fact and fiction
Beyond the infinity of black holes
Ergosphere – what?

NASA's Great Space Observatories

2 thoughts on “Cosmic retrospective — gamma ray bursts

  1. Regarding the origins of bursts and how the energy of gamma rays can vary tremendously, this Physics World article “Cosmic gamma-ray energy record shattered by high-altitude observatory” (06 Jul 2019) highlights that range.

    Cosmic gamma rays with energies as high as 450 TeV (1012 eV) have been observed by the ASgamma observatory in Tibet … This shatters the previous record of 75 TeV, which was set by the High-Energy-Gamma-Ray Astronomy observatory on the Canary Islands.

    ASgamma detected 24 gamma rays with energies in the 100-450 TeV range. The particles appear to originate in the Crab Nebula, which is a supernova remnant about 6000 light-years away. It is home to a pulsar – a rapidly rotating neutron star that broadcasts a bright beam of electromagnetic radiation.

    … the ASgamma researchers describe the Crab Nebula pulsar as “the most powerful natural electron accelerator known so far in our galaxy”.

  2. Here’s an interesting article about the speed of gamma-ray jets from cosmic beacons: Forbes > “Ask Ethan: Can Gamma-Ray Jets Really Travel Faster Than The Speed Of Light?” by Ethan Siegel, Senior Contributor (Oct 5, 2019).

    Remember that experiment (or video of a demonstration) in physics lab showing what happens to the speed of light when a laser beam is split into two paths, one through air (or vacuum) and one through water? (See this Fermilab YouTube video for an explanation of the actual physics.)

    … why, … was there a recent story claiming that gamma-ray jets, where gamma-rays themselves are a high-energy form of light, can travel faster-than-light?

    When you pass light through a medium, … its electric and magnetic fields interact with the particles in the medium, and the light is forced to move at a slower speed: the speed of light in that particular medium. … the amount that light slows down by depends on the light’s wavelength.

    [The radiation in the story] is not moving faster than c, the speed of light in a vacuum, but v, the speed of light in the particle-filled medium [matter-rich environment] surrounding the source of these gamma rays.

    What the researchers did was introduce a new, simple model that would explain the bizarre properties seen in pulsing gamma-ray bursts. They model the gamma-ray emissions as originating from a jet of fast-moving particles, which is consistent with what we know. But they then introduce a fast-moving impactor wave that runs into this expanding jet, and as the density (and other properties) of the medium changes, that wave then accelerates from moving slower-than-light to moving faster-than-light in that medium.

    [The radiation is] slower than light through the medium for one part of the journey and faster than light through the medium for another part of the journey [and is observed as separate pulses] …


    Cherenkov radiation

    Compton radiation

    UCLA Physics > YouTube video (2013) “How to Measure the Speed of Light

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