Gamma-ray bursts (GRBs) are the most powerful explosions the Universe has seen since the Big Bang. They occur approximately once per day and are brief, but intense, flashes of gamma radiation. They come from all different directions of the sky and last from a few milliseconds to a few hundred seconds. So far scientists do not know what causes them. Do they signal the birth of a black hole in a massive stellar explosion? Are they the product of the collision of two neutron stars? Or is it some other exotic phenomenon that causes these bursts?
With Swift, a NASA mission with international participation, scientists have a tool dedicated to answering these questions and solving the gamma-ray burst mystery. Its three instruments give scientists the ability to scrutinize gamma-ray bursts like never before. Within seconds of detecting a burst, Swift relays its location to ground stations, allowing both ground-based and space-based telescopes around the world the opportunity to observe the burst's afterglow. Swift is part of NASA's medium explorer (MIDEX) program and was launched into a low-Earth orbit on a Delta 7320 rocket on November 20, 2004. The Principal Investigator is Dr. Neil Gehrels (NASA-GSFC).
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Today the advanced LIGO and Virgo gravitational wave observatories announced the discovery of a new type of gravitational wave signal, likely caused by the collision of two neutron stars. The gravitational wave event occurred on 2017 August 17th, and was accompanied by a gamma-ray burst of short duration. Astronomers across the world began searching for the precise location of this event, quickly tracking it down to the nearby galaxy NGC 4993. Once pin-pointed, the Swift satellite quickly maneuvered to look at the object with its X-ray and UV/optical telescopes. The spacecraft saw no X-rays - a surprise for an event that produced higher-energy gamma rays. Instead, it found a bright and quickly fading flash of ultraviolet (UV) light. This bright UV signal was unexpected and revealed unprecedented details about the aftermath of the collision. The short-lived UV pulse likely came from material blown away by the short-lived disk of debris that powered the gamma-ray burst. The rapid fading of the UV signal suggests that this outflow was expanding with a velocity close to a tenth of the speed of light. The results of the Swift observations were published today on the journal Science. The discovery of this powerful wind was only possible using light, which is why combining gravitational waves and light in what we call 'multi-messenger astronomy' is so important.
KIC 8462852, also known as Boyajian's Star, or Tabby's Star, is one of the most mysterious stellar objects. The star has experienced unusual dips in brightness, up to 20 percent over a matter of days, and undergoes much subtler but longer-term enigmatic dimming trends. None of this behavior is expected for a normal star slightly more massive than the Sun. Speculations have included the idea that the star swallowed a planet and that it is unstable. A more imaginative theory involves an advanced civilization, which could be harvesting energy from the star and causing its brightness to decrease. A new study by Huan Meng and collaborators using NASA's Swift and Spitzer missions reveals less dimming in the infrared light from the star than in its ultraviolet light, suggesting that the cause of the dimming over long periods is likely an uneven dust cloud moving around the star.
For decades, astronomers have tried to pin down why two of the most common types of active galaxies,
known as Type I and Type II galaxies, appear different when observed from Earth. The leading theory, known
as the unified model, explains that the central black holes of Type I and Type II galaxies have the same
fundamental structure, but appear different solely because the galaxies point toward Earth at different angles.
An international team of astronomers tested this model by studying over 800 active galaxies detected by the
Burst Alert Telescope on-board Swift. Their results, published in the journal Nature, suggest that Type I
and Type II galaxies do not just appear different--they are, in fact, very different from each other.
Black holes in Type I galaxies consumes matter at a much higher rate and are therefore more efficient at emitting energy.
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