Star caught passing gas before exploding | Science News for Students

Star caught passing gas before exploding

Snapshots of light from hours after the blast give clues to star’s final year
Mar 15, 2017 — 7:10 am EST
supernova gas

In 2013, astronomers caught a glimpse of a star that exploded in the galaxy NGC7610 (background). Their observations suggest that the star passed gas (center, orange) before the blast.

Ofer Yaron

A star on the brink of death may have been spurting gas for about a year before it exploded, a new study concludes. That comes as a bit of a surprise. Most scientists had assumed the first symptom of a supernova would be the stellar explosion itself.

Three and a half years ago, astronomers caught a glimpse of a star exploding. It was just a few hours after light from the blast first reached Earth.

This was early, astronomers note. “Several years ago, to catch a supernova early would mean to detect it at several days, a week, or maybe more, after the explosion,” says Ofer Yaron. He is an astrophysicist at the Weizmann Institute of Science in Rehovot, Israel. Now, he says,  “we talk about day one" when referring to early observations.

Previous supernovas had been spotted this early. But scientists got something extra with this new one: its spectrum. That’s a measurement of the light emitted from the blast, by wavelength (color). The spectrum was measured just six hours after the blast.

The star had blown apart in a type 2 supernova. Such an explosion is triggered by the collapse of a dying star.

Yaron and his colleagues spotted the stellar fireworks with the Intermediate Palomar Transient Factory. Their search used surveys of the sky by a telescope at the Palomar Observatory, near San Diego. The supernova appeared on October 6, 2013 in a galaxy called NGC7610. It resides 166 million light-years from Earth.

The researchers measured the star’s spectrum at several intervals after the supernova got underway. Those data painted a picture of what happened before and after the blast.

As the star exploded, a violent shock wave ripped through the surrounding gas. So violent was the shock wave that it stripped electrons from atoms. Those electrons and atoms later recombined. And when they did, the atoms emitted certain wavelengths, or spectra, of light.

From these spectra, the scientists deduced that the gas outside the star had been emitted before the explosion. Perhaps as much as a year or so before the blast. Yaron and his colleagues described their calculations online February 13 in Nature Physics.

“This is actually very exciting,” says Matteo Cantiello. He is an astrophysicist at the Center for Computational Astrophysics in New York City, and was not involved in the new work. For typical stars on the brink of collapse, “this is the first clear evidence that … the last period of their lives is not quiet,” he says. In fact, he says, it now appears that dying stars may become unstable and rapidly spurt out material.

“That's very, very odd,” agrees Peter Garnavich. He is an astrophysicist at the University of Notre Dame in Indiana. Scientists typically assume that what happens in the outer layers of stars about to explode have little to do with activities inside the star. The new observations suggest the two are connected, he says. But how an oncoming collapse could provoke the star to spew gas before a star explodes in a supernova, he says, remains unknown.

Power Words

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astrophysics      An area of astronomy that deals with understanding the physical nature of stars and other objects in space. People who work in this field are known as astrophysicists.

atom     The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

electron   A negatively charged particle, usually found orbiting the outer regions of an atom; also, the carrier of electricity within solids.

galaxy    A massive group of stars bound together by gravity. Galaxies, which each typically include between 10 million and 100 trillion stars, also include clouds of gas, dust and the remnants of exploded stars.

light-year   The distance light travels in one year, about 9.48 trillion kilometers (almost 6  trillion miles). To get some idea of this length, imagine a rope long enough to wrap around the Earth. It would be a little over 40,000 kilometers (24,900 miles) long. Lay it out straight. Now lay another 236 million more that are the same length, end-to-end, right after the first. The total distance they now span would equal one light-year.

shock waves      Tiny regions in a gas or fluid where properties of the host material change dramatically owing to the passage of some object (which could be a plane in air or merely bubbles in water). Across a shock wave, a region’s pressure, temperature and density spike briefly, and almost instantaneously.

spectrum     (plural: spectra) A range of related things that appear in some order. (in light and energy) The range of electromagnetic radiation types; they span from gamma rays to X rays, ultraviolet light, visible light, infrared energy, microwaves and radio waves.

supernova    (plural: supernovae or supernovas) A massive star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass.

type 2 supernova    This occurs when nuclear fusion can no longer continue in the core of a massive star because the core has burned through its fuel (and in the process created new elements, via fusion).

wavelength    The distance between one peak and the next in a series of waves, or the distance between one trough and the next. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.

Citation

Journal:​ ​​ O. Yaron et al. Confined dense circumstellar material surrounding a regular type II supernova. Nature Physics. Published online February 13, 2017. doi: 10.1038/nphys4025.