A supermassive black hole at the core of the giant elliptical galaxy M87 ejects a hot, bright plasma that flies through space at nearly the speed of light. It makes the "Death Star" beam from the Star Wars trilogy look like an insignificant candle lighter. Hubble astronomers have found that it seems dangerous to get close to a high-energy plasma jet.
This is the artist's vision of the core of the giant elliptical galaxy M87. A supermassive black hole ejects a 3,000-light-year-long jet of plasma, traveling almost at the speed of light. To the right of the foreground is a binary star system. The system is far from the black hole, but near the jet stream. In this system, an aging, expanding normal star spills hydrogen gas into a burned-out white dwarf companion. As hydrogen accumulates on the surface of the white dwarf, it reaches a tipping point where it explodes like a hydrogen bomb. In this huge galaxy of a trillion stars, novae erupt frequently, but novae near the jet stream appear to erupt more frequently. As for why the black hole jet increases the frequency of nova explosions, no one can say clearly. Source: NASA, ESA, Joseph Olmsted (STScI)
In the vicinity of the jet's 3,000-light-year trajectory, stars appear to explode more frequently. These stars, known as novae, erupt in a binary system in which an aging, expanding normal star spills hydrogen gas into a burned-out white dwarf companion. As hydrogen accumulates on the surface of the white dwarf, it reaches a tipping point where it explodes like a hydrogen bomb. Novas often explode in this megagalaxy of a trillion stars, but novas near the jet appear to explode more often.
Astronomers speculate that some effect of the jet either enhances the fuel supply process and explosion velocity of the nova, or breeds new nova binary stars in its vicinity. But once astronomers "counted the numbers," both hypotheses failed. Therefore, it is still unknown why the black hole jet increases the velocity of nova explosions.
Images of the giant galaxy M87 taken by the Hubble Space Telescope show a 3,000-light-year jet of plasma ejecting from the galaxy's central black hole with 6.5 billion solar masses. The blowtorch-like jet stream seems to cause the star to erupt along its trajectory. These novae were not swept up in the jet, but were apparently in a danger zone near the jet. During a recent nine-month survey, astronomers using the Hubble telescope found that twice as many novae were occurring near the jet stream as elsewhere in the Milky Way. The Milky Way is home to trillions of stars and thousands of star-like star clusters. Sources: NASA, ESA, STScI, Alec Lessing (Stanford University), Mike Shara (AMNH), Edward Baltz (Stanford University), Joseph DePasquale (STScI)
Using United States' NASA's Hubble Space Telescope, astronomers have made a startling discovery: Blowtorch-like jets from supermassive black holes at the core of a massive galaxy appear to cause stars to erupt along their tracks. The stars, known as "novae," are not swept up in the jets, but are apparently in a dangerous neighborhood nearby.
The discovery has puzzled researchers who are looking for an explanation. Alec Lessing of Stanford University is the first author of the paper, published Sept. 27 in the Journal of Astrophysics. This means that our understanding of how black hole jets interact with their surroundings is missing something."
Nova erupt in a binary star system in which an aging, expanding normal star spills hydrogen gas into a burned-out white dwarf companion. When the surface area of a white dwarf gathers a mile-deep hydrogen layer, the hydrogen layer explodes like a giant nuclear bomb. The white dwarf is not destroyed by the nova explosion, its surface is ejected out, and then it continues to draw fuel from its companions, and the cycle of the nova explosion begins again.
Hubble found that during the survey, twice as many novae erupted near the jet stream as elsewhere in the giant galaxy. The jet is emitted by a central black hole with 6.5 billion solar masses, and the black hole is surrounded by a disk of swirling material. The black hole is filled with falling matter, ejecting 3,000 light-years of plasma through space at nearly the speed of light. Anything hit by a high-energy beam will be scorched. But, according to Hubble's new findings, an explosive outflow near it is also clearly risky.
This video depicts the location of the nova – the exploding star – observed by the Hubble Space Telescope in the giant elliptical galaxy M87. The most striking feature of the galaxy is a 3,000-light-year jet of plasma ejected from a supermassive central black hole. Hubble observations have discovered a number of novae in the vicinity of the jet. When the nova explodes, the red circle turns white. Stars near the jet appear to explode more frequently. The jet stream may have pushed interstellar hydrogen to neighboring stars, enhancing the star's fueling process and thus increasing the frequency of explosions. When photometric measurements are taken across galaxies, fewer novae appear farther away from the jet. Sources: NASA, ESA, Joseph DePasquale (STScI).
Finding twice as many novae in the vicinity of the jet means that twice as many novae are forming binary star systems in the vicinity of the jet, or that these systems erupt twice as often as similar systems elsewhere in the Milky Way.
"The jet stream does something to the star system that wanders into the surrounding neighboring areas. "Maybe the jets somehow spray hydrogen fuel onto white dwarfs, causing them to erupt more often," Lessing said. But it's not clear that this is a physical push. This can be caused by the pressure of the light emitted by the ejector. The faster the hydrogen is transported, the faster the burst will be. There may be something that doubles the rate of mass transfer on white dwarfs near the jet. Another idea the researchers are considering is that the jet stream is heating the white dwarf's companion star, causing it to overflow further and dumping more hydrogen into the white dwarf. However, the researchers calculated that the degree of heating was not enough to produce this effect. "
Images of the giant galaxy M87 taken by the Hubble Space Telescope (with color markers, scale bars, and compass) show a 3,000-light-year stream of plasma ejecting from the galaxy's 6.5 billion solar mass of the central black hole. The blowtorch-like jet stream seems to cause the star to erupt along its trajectory. These novae were not swept up in the jet, but were apparently in a danger zone near the jet. During a recent nine-month survey, astronomers using the Hubble telescope found that there were twice as many novae near the jet stream as elsewhere in the Milky Way. The Milky Way is home to trillions of stars and thousands of star-like globular clusters. Sources: NASA, ESA, Alec Lessing (Stanford University), Edward Baltz (Stanford University), Mike Shara (AMNH), Joseph DePasquale (STScI)
Michael Shara, co-researcher at the United States Museum of Natural History in New York City, said: "We're not the first to say there seems to be more activity around the M87 jet. But Hubble shows this enhanced activity with more examples and statistical significance than we have before. "
Shortly after the launch of the Hubble telescope in 1990, astronomers used their first generation of tiny astronomical cameras (FOCs) to peek into the center of M87, where a massive black hole lurks. They noticed something unusual happening around the black hole. Almost every time Hubble observed, astronomers were able to see pale blue "transient events" that could be evidence of a nova, like the camera flashes of nearby paparazzi. But the FOC has a very narrow field of view, and Hubble astronomers can't take their eyes off the ejection zone and compare it to the vicinity of the ejection zone. For more than two decades, these results have been mysterious and enticing.
In the nine months that Hubble has been observing the nova with newer, wider-angle cameras, strong evidence has been collected for the effect of jets on the stars of the host galaxy. This is a challenge to the telescope's observation schedule, as it requires M87 to be revisited precisely every five days to take another snapshot. Add up all the M87 images and you get the deepest M87 image ever.
Hubble discovered 87 novae in the M94, which can be captured by its camera. "Jets aren't the only thing we're looking at – we're looking at the entire inner galaxy. Once you've mapped all known novae on top of M87, you don't need statistics to convince yourself that there are an excess of novae along the jet. This is not rocket science. We made discoveries just by looking at the images. Although we were really surprised, our statistical analysis of the data confirmed what we saw clearly," said Salad.
This achievement is entirely due to the unique capabilities of the Hubble telescope. The images taken by ground-based telescopes are not clear and it is not possible to see novae in the depths of M87. They can't tell a star or stellar explosion close to the core of a galaxy because the environment around the black hole is too bright. Only Hubble can detect novae against the background of bright M87.
Nova are very common in the universe, and every day a nova explodes somewhere in M87. However, since there are at least 100 billion galaxies in the entire visible universe, about 1 million new stars explode somewhere in the universe every second.
编译自/SciTechDaily