By Sanjeev Kumar Patro
Bhubaneswar: There is a much popular bollywood song in Rajesh Khanna’s Kati Patang, where melodious Kishore da singing “Shama Kahe Parwane se pare chale ja… meri tarah jal jayega… yahan Nahin aa… woh nahi sunta hai.. usko jal jana hota hai..” This ‘Shama-Parwana’ story – the story of small insects/flies getting attracted to a blaze of light is not a story in the ether world only, NASA’s Hubble has discovered this ‘sama-parwana’ story in space, too.
But the twist in the tale is, here the ‘parwanas’, though hover around the danger zone, never get burnt up.
OVER TO NASA FINDINGS
In a surprise finding, astronomers using NASA's HubbleSpace Telescope have discovered a blowtorch-like jet from a supermassive black hole at the core of a huge galaxy that seems causing stars to erupt along its trajectory. The stars, called novae, are not caught inside the jet, but apparently in a dangerous neighborhood nearby.
The finding is confounding researchers searching for an explanation. "We don't know what's going on, but it's just a very exciting finding," said Alec Lessing of Stanford University, lead author of the paper published in The Astrophysical Journal. “This means there's something missing from our understanding of how black hole jets interact with their surroundings, he added."
WHAT ARE NOVAE?
A nova is a strong, rapid increase in the brightness of a star. The word comes from the latin for "new star," because often a star previously too dim to be seen with the naked eye can become the brightest object in the sky (besides the sun and the moon) when it becomes a nova.
Novae are remarkably common in the universe. One nova erupts somewhere in M87 every day. But since there are at least 100 billion galaxies throughout the visible universe, around 1 million novae erupt every second somewhere out there.
Nova erupts in a double-star system where an aging, swelled-up, normal star spills hydrogen onto a burned-out white dwarf companion star. When the dwarf has tanked up a mile-deep surface layer of hydrogen that layer explodes like a giant nuclear bomb. The white dwarf isn't destroyed by the nova eruption, which ejects its surface layer and then goes back to siphoning fuel from its companion, and the nova-outburst cycle starts over again.
Hubble found twice as many novae going off near the jet as elsewhere in the giant galaxy during the surveyed time period. The jet is launched by a 6.5-billion-solar-mass central black hole surrounded by a disk of swirling matter. The black hole, engorged with infalling matter, launches a 3,000-light-year-long jet of plasma blazing through space at nearly the speed of light. Anything caught in the energetic beam would be sizzled. But being near its blistering outflow is apparently also risky, according to the new Hubble findings.
The finding of twice as many novae near the jet implies that there are twice as many nova-forming double-star systems near the jet or that these systems erupt twice as often as similar systems elsewhere in the galaxy.
"There's something that the jet is doing to the star systems that wander into the surrounding neighborhood. Maybe the jet somehow snowplows hydrogen fuel onto the white dwarfs, causing them to erupt more frequently," said Lessing. "But it's not clear that it's a physical pushing. It could be the effect of the pressure of the light emanating from the jet. When you deliver hydrogen faster, you get eruptions faster. Something might be doubling the mass transfer rate onto the white dwarfs near the jet." Another idea the researchers considered is that the jet is heating the dwarf's companion star, causing it to overflow further and dump more hydrogen onto the dwarf. However, the researchers calculated that this heating is not nearly large enough to have this effect.
"We're not the first people who've said that it looks like there's more activity going on around the M87 jet," said co-investigator Michael Shara of the American Museum of Natural History in New York City. "But Hubble has shown this enhanced activity with far more examples and statistical significance than we ever had before."
20-Year Mystery Solved!
Shortly after Hubble's launch in 1990, astronomers used its first-generation Faint Object Camera (FOC) to peer into the center of M87 where the monster black hole lurks. They noted that unusual things were happening around the black hole. Almost every time Hubble looked, astronomers saw bluish "transient events" that could be evidence for novae popping off like camera flashes from nearby paparazzi. But the FOC's view was so narrow that Hubble astronomers couldn't look away from the jet to compare with the near-jet region. For over two decades, the results remained mysteriously tantalizing.
Compelling evidence for the jet's influence on the stars of the host galaxy was collected over a nine-month interval of Hubble observing with newer, wider-view cameras to count the erupting novae. This was a challenge for the telescope's observing schedule because it required revisiting M87 precisely every five days for another snapshot. Adding up all of the M87 images led to the deepest images of M87 that have ever been taken.
Hubble found 94 novae in the one-third of M87 that its camera can encompass. "The jet was not the only thing that we were looking at — we were looking at the entire inner galaxy. Once you plotted all known novae on top of M87 you didn't need statistics to convince yourself that there is an excess of novae along the jet. This is not rocket science. We made the discovery simply by looking at the images. And while we were really surprised, our statistical analyses of the data confirmed what we clearly saw," said Shara.
PAT ON HUBBLE
The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, Colorado, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, Maryland, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
