- 2956 - GAMMA RAY BURSTS - - Long ago and far across the universe, an enormous burst of gamma rays unleashed more energy in a half-second than the sun will produce over its entire 10-billion-year lifetime. ½ second versus 10,000,000,000 years! The light got here on May 22, 2020,
- This is a test. How many of your 4th graders can get the right answers? How many of the faculty?
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- 5 questions, you are allowed 10 seconds for each, the most right answers with the fastest times is the honor student for the day.
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- Question 1: You are participating in a race. You overtake the second person. What position are you in?
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- Question 2: What about if you overtake the last person in the race?
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- Question 3: Math in your head, no calculators allowed. Take 1000 and add 40 to it. Now add another 1000. Now add 30. Add another 1000. Now add 20. Now add another 1000. Now add 10. What is the total?
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- Question 4: Mary’s father has five daughters Nana, Nene, Nini, Nono, what is the name of the 5th daughter?
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- Question 5: A mute person who wants to buy a toothbrush begins imitating the action of brushing one’s teeth. He successfully expresses himself to the shopkeeper who helps him with the purchase. Next a blind man comes in wishing to by a pair of sunglasses, how can he express himself to the shopkeeper?
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- Times up:
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- (1) You are second
- (2) How can you overtake the last person?
- (3) 4100
- (4) Mary
- (5) Simply ask the shopkeeper.
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- After examining the incredibly bright burst with optical, X-ray, near-infrared and radio wavelengths, astrophysists believe it potentially spotted the birth of a “magnetar“.
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- They believe the magnetar was formed by two neutron stars merging, which has never before been observed. The merger resulted in a brilliant “kilo nova“, the brightest ever seen, whose light finally reached Earth on May 22, 2020. The light first came as a blast of gamma-rays, called a short gamma-ray burst.
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- Gamma Rays are high energy light that has very short wavelengths and therefore high energy.
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- When two neutron stars merge, the most common predicted outcome is that they form a heavy neutron star that collapses into a blackhole within milliseconds. For this particular short gamma-ray burst, the heavy object survived. Instead of collapsing into a blackhole, it became a “magnetar“
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- A magnetar is a rapidly spinning “neutron star” that has large magnetic fields, dumping energy into its surrounding environment and creating the very bright glow that we can see.
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- After the light was first detected by NASA's Neil Gehrels Swift Observatory, scientists quickly enlisted other telescopes, including NASA's Hubble Space Telescope, the Very Large Array, the W.M. Keck Observatory and the Las Cumbres Observatory Global Telescope network, to study the explosion's aftermath and its host galaxy.
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- Compared to X-ray and radio observations, the near-infrared emission detected with Hubble was much too bright, 10 times brighter than predicted.
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- As the data were coming in from the Hubble observations astronomers had to figure out about what that meant for the physics behind these extremely energetic explosions. This was a magnetic monster.
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- There were several possibilities to explain the unusual brightness, known as a short gamma-ray burst, that Hubble saw. Researchers think short bursts are caused by the merger of two neutron stars, extremely dense objects about the mass of the sun compressed into the volume of a large city like Chicago.
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- While most short gamma-ray bursts result in a blackhole, the two neutron stars that merged in this case may have combined to form a magnetar, a supermassive neutron star with a very powerful magnetic field.
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- This magnetar-powered kilonova, whose peak brightness reaches up to 10,000 times that of a classical nova.
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------------------ 1) Two orbiting neutron stars spiral closer and closer together.
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----------------- 2) They collide and merge, triggering an explosion that unleashes more energy in a half-second than the Sun will produce over its entire 10-billion-year lifetime.
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----------------- 3) The merger forms an even more massive neutron star called a magnetar, which has an extraordinarily powerful magnetic field.
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----------------- 4) The magnetar deposits energy into the ejected material, causing it to glow unexpectedly bright at infrared wavelengths.
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- Magnetic field lines are anchored to the star and are whipping around at about 1,000 times a second, and this produces a magnetized wind. These spinning field lines extract the rotational energy of the neutron star formed in the merger, and deposit that energy into the ejecta from the blast, causing the material to glow even brighter.
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- Most magnetars are formed in the explosive deaths of massive stars, leaving these highly magnetized neutron stars behind. However, it is possible that a small fraction form in neutron star mergers.
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- Kilonovae, which are typically 1,000 times brighter than a classic nova, are expected to accompany short gamma-ray bursts. Unique to the merger of two compact objects, kilonovae glow from the radioactive decay of heavy elements ejected during the merger, producing elements like gold and uranium.
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- The unexpected brightness seen by Hubble came from a magnetar that deposited energy into the kilonova material, then, within a few years, the ejected material from the burst will produce light that shows up at radio wavelengths. Follow-up radio observations may ultimately prove that this was a magnetar, leading to an explanation of the origin of such objects.
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- The final chapter of the historic detection of the powerful merger of two neutron stars in 2017 officially has been written. After the extremely bright burst finally faded to black, an international team led by Northwestern University painstakingly constructed its afterglow—the last bit of the famed event's life cycle.
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- Not only is the resulting image the deepest picture of the neutron star collision's afterglow to date, it also reveals secrets about the origins of the merger, the jet it created and the nature of shorter gamma ray bursts.
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- This is the deepest exposure we have ever taken of this event in visible light. Many scientists consider the 2017 neutron-star merger, dubbed GW170817, as LIGO's (Laser Interferometer Gravitational-Wave Observatory) most important discovery to date.
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- It was the first time that astrophysicists captured two neutron stars colliding. Detected in both gravitational waves and electromagnetic light, it also was the first-ever multi-messenger observation between these two forms of radiation.
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- The light from GW170817 was detected, partly, because it was nearby, making it very bright and relatively easy to find. When the neutron stars collided, they emitted a kilo nova, light 1,000 times brighter than a classical nova, resulting from the formation of heavy elements after the merger. But it was exactly this brightness that made its afterglow, formed from a jet traveling near light-speed, pummeling the surrounding environment.
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- 100 days after the merger, the kilonova had faded into oblivion, and the afterglow took over. The afterglow was so faint, however, leaving it to the most sensitive telescopes to capture it.
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- Starting in December, 2017, NASA's Hubble Space Telescope detected the visible light afterglow from the merger and revisited the merger's location 10 more times over the course of a year and a half. At the end of March 2019 Hubble was able to obtain the final image and the deepest observation to date.
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- Over the course of seven-and-a-half hours, the telescope recorded an image of the sky from where the neutron-star collision occurred. The resulting image showed, 584 days after the neutron-star merger, that the visible light emanating from the merger was finally gone.
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- By using all 10 images, in which the kilonova was gone and the afterglow remained as well as the final, deep Hubble image without traces of the collision. The team overlaid their deep Hubble image on each of the 10 afterglow images. Then, using an algorithm, they meticulously subtracted, pixel by pixel, all light from the Hubble image from the earlier afterglow images.
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- The final time-series of images, showing the faint afterglow without light contamination from the background galaxy. Completely aligned with model predictions, it is the most accurate imaging time-series of GW170817's visible-light afterglow produced to date.
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- The brightness evolution perfectly matches our theoretical models of jets. It also agrees perfectly with what the radio and X-rays are telling us.
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- The cosmic explosions known as short gamma ray bursts are actually neutron star mergers, just viewed from a different angle. Both produce relativistic jets, which are like a fire hose of material that travels near the speed of light. Astrophysicists typically see jets from gamma ray bursts when they are aimed directly, like staring directly into the fire hose. But GW170817 was viewed from a 30-degree angle, which had never before been done in the optical wavelength.
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- GW170817 is the first time we have been able to see the jet 'off-axis. The new time-series indicates that the main difference between GW170817 and distant short gamma-ray bursts is the viewing angle.
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December 29, 2020 GAMMA RAY BURSTS - 2956
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--------------------- --- Tuesday, December 29, 2020 ---------------------------
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