Reverse Shockwave, Moving At Mach 1,000, Illuminates The Remains Of Tycho Supernova
When Tycho Brahe, the 16th century Danish astronomer, looked up and saw a new star in the sky, the discovery was disarming. Astronomers had believed the sky to be fixed, the celestial bodies permanent and unchanged. A year later, in 1573, Brahe published De Nova Stella, or "new star." Later, they named that star Tycho.
What he and other early astronomers saw was a supernova, the exploding death of a massive star too far away to be previously observed. More than 400 years later, however, scientists can still "see" the Tycho supernova remains through X-ray emissions. But until now, no one could explain why those particulate remnants were illuminated.
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Researchers at the Harvard-Smithsonian Center for Astrophysics have discovered that a reverse shockwave, moving at speeds of about Mach 1,000, is interacting with the supernova nebula and causing it to release heat and X-ray light. Mach 1,000 is equal to 761,207 mph, or a little more than one-thousandth the speed of light. "We wouldn't be able to study ancient supernova remnants without a reverse shock to light them up," says Hiroya Yamaguchi, who conducted this research, in a statement.
A shockwave, like a sound wave or an ocean wave, is a ripple of energy moving through a medium. The story of Tycho's shockwave goes like this: First, Tycho was a white dwarf, a tiny but extremely massive old star, that suddenly exploded when it collided with a nearby star. The explosion, called a supernova, sent silicon, iron, and other elements hurtling into space at 11 million mph. In the vacuum of space, without a medium, that's not a shockwave.
The shockwave happened, like a mega sonic boom, when the supernova debris collided with interstellar gas. Hundreds of years later, that shock wave is still traveling at 300 times the speed of sound. But like the reverberating ripples in a swimming pool, the wave reversed. That reverse shockwave is moving at 1,000 times the speed of sound and allowing scientists to capture X-ray images of Tycho, like the one above. Randall Smith, a co-author of the study, which was accepted for publication in The Astrophysical Journal, described it in layman's terms: "It's like the wave of brake lights that marches up a line of traffic after a fender-bender on a busy highway."
"Their observations represent the first clear evidence for such efficient, 'collisionless' electron heating at the reverse shock of Tycho's supernova remnant," the Harvard-Smithsonian Center said. Rather than producing heat and light through the collision of molecules, the Harvard-Smithsonian scientists said the reaction here is similar to the chemical process that illuminates a fluorescent light, except this produces X-rays outside the visible spectrum. "Thanks to the reverse shock, Tycho's supernova keeps on giving," Smith said.
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