Posted on by Ray Sanders

A Psychedelic Guide to Tycho’s Supernova Remnant

Gamma-rays detected by Fermi's LAT show that the remnant of Tycho's supernova shines in the highest-energy form of light. This portrait of the shattered star includes gamma rays (magenta), X-rays (yellow, green, and blue), infrared (red) and optical data. Image Credit: Gamma ray, NASA/DOE/Fermi LAT Collaboration; X-ray, NASA/CXC/SAO; Infrared, NASA/JPL-Caltech; Optical, MPIA, Calar Alto, O. Krause et al. and DSS)

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By no means are we suggesting that NASA’s Fermi Gamma-Ray Space Telescope can induce altered states of awareness, but this ‘far-out’ image is akin to 1960’s era psychedelic art. However, the data depicted here provides a new and enlightened way of looking at an object that’s been observed for over 400 years. After years of study, data collected by Fermi has revealed Tycho’s Supernova Remnant shines brightly in high-energy gamma rays.

The discovery provides researchers with additional information on the origin of cosmic rays (subatomic particles that are on speed). The exact process that gives cosmic rays their energy isn’t well understood since charged particles are easily deflected by interstellar magnetic fields. The deflection by interstellar magnetic fields makes it impossible for researchers to track cosmic rays to their original sources.

“Fortunately, high-energy gamma rays are produced when cosmic rays strike interstellar gas and starlight. These gamma rays come to Fermi straight from their sources,” said Francesco Giordano at the University of Bari in Italy.

But here’s some not-so-psychedelic facts about supernova remnants in general and Tycho’s in particular:

When a massive star reaches the end of its lifetime, it can explode, leaving behind a supernova remnant consisting of an expanding shell of hot gas propelled by the blast shockwave. In many cases, a supernova explosion can be visible on Earth – even in broad daylight. In November of 1572, a new “star” was discovered in the constellation Cassiopeia. The discovery is now known to be the most visible supernova in the past 400 years. Often called “Tycho’s supernova”, the remnant shown above is named after Danish astronomer Tycho Brahe, who spent a great deal of time studying the supernova.

Tycho's map shows the supernova's position (largest symbol, at top) relative to the stars that form Cassiopeia. Image credit: University of Toronto
The 1572 supernova event occurred when the night sky was considered to be a fixed and unchanging part of the universe. Tycho’s account of the discovery gives a sense of just how profound his discovery was. Regarding his discovery, Tycho stated, “When I had satisfied myself that no star of that kind had ever shone forth before, I was led into such perplexity by the unbelievability of the thing that I began to doubt the faith of my own eyes, and so, turning to the servants who were accompanying me, I asked them whether they too could see a certain extremely bright star…. They immediately replied with one voice that they saw it completely and that it was extremely bright”

In 1949, physicist Enrico Fermi (the namesake for the Fermi Gamma-ray Space Telescope) theorized that high-energy cosmic rays were accelerated in the magnetic fields of interstellar gas clouds. Following up on Fermi’s work, astronomers learned that supernova remnants might be the best candidate sites for magnetic fields of such magnitude.

One of the main goals of the Fermi Gamma-ray Space Telescope is to better understand the origins of cosmic rays. Fermi’s Large Area Telescope (LAT) can survey the entire sky every three hours, which allows the instrument to build a deeper view of the gamma-ray sky. Since gamma rays are the most energetic form of light, studying gamma ray concentrations can help researchers detect the particle acceleration responsible for cosmic rays.

Co-author Stefan Funk (Kavli Institute for Particle Astrophysics and Cosmology) adds, “This detection gives us another piece of evidence supporting the notion that supernova remnants can accelerate cosmic rays.”

After scanning the sky for nearly three years, Fermi’s LAT data showed a region of gamma-ray emissions associated with the remnant of Tycho’s supernova. Keith Bechtol, (KIPAC graduate student) commented on the discovery, saying, “We knew that Tycho’s supernova remnant could be an important find for Fermi because this object has been so extensively studied in other parts of the electromagnetic spectrum. We thought it might be one of our best opportunities to identify a spectral signature indicating the presence of cosmic-ray protons”

The team’s model is based on LAT data, gamma-rays mapped by ground-based observatories and X-ray data. The conclusion the team has come to regarding their model is that a process called pion production is the best explanation for the emissions. The animation below depicts a proton moving at nearly the speed of light and striking a slower-moving proton. The protons survive the collision, but their interaction creates an unstable particle — a pion — with only 14 percent of the proton’s mass. In 10 millionths of a billionth of a second, the pion decays into a pair of gamma-ray photons.

If the team’s interpretation of the data is accurate, then within the remnant, protons are being accelerated to near the speed of light. After being accelerated to such tremendous speeds, the protons interact with slower particles and produce gamma rays. With all the amazing processes at work in the remnant of Tycho’s supernova, one could easily imagine how impressed Brahe would be.

And no tripping necessary.

Learn more about the Fermi Gamma-ray Space Telescope at: http://www.nasa.gov/mission_pages/GLAST/main/index.html

Source: Fermi Gamma-ray Space Telescope Mission News

Posted on by Nancy Atkinson

What Triggers a Type Ia Supernova? Chandra Finds New Evidence

This Chandra image of the Tycho supernova remnant contains new evidence for what triggered the original supernova explosion. Credit: NASA/CXC/Chinese Academy of Sciences/F. Lu et al.

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What makes a star go boom? A new look at Tycho’s supernova remnant by the Chandra X-ray telescope has supplied astronomers with previously unseen evidence for what could trigger specific type of supernova, a Type Ia supernova explosion. Astronomers have spotted what appears to be material that was blasted off a companion star to a white dwarf when it exploded, creating the supernova seen by Danish astronomer Tycho Brahe in 1572. There is also evidence that this material blocked the explosion debris, creating an “arc” and a “shadow” in the supernova remnant.

There are two main types of supernovae. One is where a massive star – much bigger than our sun — burns all its nuclear fuel and collapses in on itself, which ignites a supernova explosion. Type Ia supernovae, however, are different. Smaller stars eventually turn into white dwarfs at the end of their lives, becoming an ultra-dense ball of carbon and oxygen about the size of the Earth, with the mass of our Sun. In some instances, though, a white dwarf somehow ignites, creating an explosion so bright that it can be seen billions of light years away, across much of the Universe. But astronomers really haven’t understood what causes these explosions to start.

There are a couple of popular theories: one scenario for Type Ia supernovas involves the merger of two white dwarfs. In this case, no companion star or evidence for material blasted off a companion should exist. In the other theory, a white dwarf pulls material from a “normal,” or Sun-like, companion star until a thermonuclear explosion occurs.

Both scenarios may actually occur under different conditions, but the latest Chandra result from Tycho supports the latter one.

This is an artist's impression showing an explanation from scientists for the origin of an X-ray arc in Tycho's supernova remnant. Credit: NASA/CXC/M.Weiss

The new Chandra images show the famous leftovers of Tycho’s supernova, and reveal for the first time an arc of X-ray emission within the supernova remnant. The shape of the arc is different from any other feature seen in the remnant. This supports the conclusion that a shock wave created the arc when a white dwarf exploded and blew material off the surface of a nearby companion star.

In addition, this new study seems to show how resilient some stars can be, as the supernova explosion appears to have blasted very little material off the companion star. Previously, studies with optical telescopes have revealed a star within the remnant that is moving much more quickly than its neighbors, hinting that it could be the missing companion.

“It looks like this companion star was right next to an extremely powerful explosion and it survived relatively unscathed,” said Q. Daniel Wang of the University of Massachusetts in Amherst, a member of the research team whose paper will appear in the May 1st issue of The Astrophysical Journal. “Presumably it was also given a kick when the explosion occurred. Together with the orbital velocity, this kick makes the companion now travel rapidly across space.”

This image shows iron debris in Tycho's supernova remnant. The site of the supernova explosion is shown, as inferred from the motion of the possible companion to the exploded white dwarf. The position of material stripped off the companion star by the explosion, and forming an X-ray arc, is shown by the white dotted line. This structure is most easily seen in an image showing X-rays from the arc's shock wave. Finally, the arc has blocked debris from the explosion creating a "shadow" in the debris between the red dotted lines, extending from the arc to the edge of the remnant. Credit: NASA/CXC/Chinese Academy of Sciences/F. Lu et al.

Using the properties of the X-ray arc and the candidate stellar companion, the team determined the orbital period and separation between the two stars in the binary system before the explosion. The period was estimated to be about 5 days, and the separation was only about a millionth of a light-year, or less than a tenth the distance between the Sun and the Earth. In comparison, the remnant itself is about 20 light-years across.

Other details of the arc support the idea that it was blasted away from the companion star. For example, the X-ray emission of the remnant shows an apparent “shadow” next to the arc, consistent with the blocking of debris from the explosion by the expanding cone of material stripped from the companion.

“This stripped stellar material was the missing piece of the puzzle for arguing that Tycho’s supernova was triggered in a binary with a normal stellar companion,” said Fangjun Lu of the Institute of High Energy Physics, Chinese Academy of Sciences in Beijing. “We now seem to have found this piece.”

Because Type Ia supernova are all of similar brightness, they are used as a standard candle to measure the expansion of the Universe, and this new observation by Chandra has helped to answer at least part of the long-standing – and critical — question of what triggers these bright explosions.

Source: Chandra