New Research Suggests that the Fermi Bubbles are Not Emitting Mysterious Gamma Rays
By: April Carson
A gamma-ray trickster has just been discovered near the Milky Way. Energetic radiation that was previously linked to structures erupting from the Milky Way's galactic centre, known as the Fermi bubbles, is actually coming from something farther away.
The origins are thought to be tiny dwarf galaxies orbiting our own, with millisecond pulsars at their centers. The discovery has implications for our comprehension of the Fermi bubbles, but it may also have an impact on other disciplines, such as dark matter research.
This latest gamma-ray finding was made using data from the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. LAT detects high-energy photons, or gamma rays, emitted by some of the most extreme and energetic objects in the Universe.
Discovered in 2010, the Fermi bubbles were a huge surprise. They are gargantuan bubbles of high-energy gas emanating from the galactic center that extend above and below the galactic plane, for a total distance of 50,000 light-years. The expansion rate is estimated to be millions of miles an hour.
Researchers believe that the bubbles were created millions of years ago by the supermassive black hole at the center of our galaxy. The bubbles have been expanding outward ever since and are brighter in high-energy gamma radiation than other parts of our galaxy.
The radiation from the Fermi bubbles is not evenly distributed. In particular, there is a "cocoon" of cosmic rays that were freshly accelerated in the southern lobe. This was interpreted as being part of the superbubble environment when it was discovered in 2011.
A team of curious astronomers, with Roland Crocker as their leader and astrophysicist, from the Australian National University in Australia has made an interesting discovery. Crocker and his team think that the Fermi Bubbles might not be emitting the strange gamma rays after all, as was previously thought.
The cocoon's positioning is an accurate match with another object's location – the center of Sagittarius dwarf spheroidal galaxy. This galaxy is a small satellite of the Milky Way and it's currently being destroyed as it becomes one with the larger galactic system.
An odd-shaped galaxy that rotates counterclockwise, but has no designated name. This might be a coinkydink with a likelihood of less than 1 percent. But it gets even more intriguing. The Sagittarius galaxy and the cocoon have similar forms and orientations, as well.
The evidence isn't conclusive, but the research is pointing more and more towards the idea that the Fermi Bubbles aren't emitting anything strange after all – rather, they're just reflecting light from another object.
Without an understanding of how much light something emits, it is difficult to discern its distance.
If you see an object releasing gamma radiation within a larger structure of gamma radiation, it's probably safe to assume that the two are related. But if two things with similar shapes and orientations were to line up perfectly in our line of sight, that would be quite odd.
More likely than not, there is a link between those two objects.
The scientists decided to re-examine the cocoon and see whether the dwarf galaxy might be a possible answer for the gamma radiation discovered there.
First, they looked at the possibility that the Fermi Bubbles were actually much closer to us than had been previously thought.
But the new data showed that this was not the case.
The second possibility was that the gamma rays coming from the cocoon were actually emitted by something within it, rather than from the cocoon itself.
The emission was modeled over a variety of explanations, including the intra-bubble cocoon and the Sagittarius galaxy. They found that by quite some significance, the most likely emitter of gamma radiation in the Fermi cocoon was actually coming from the Sagittarius galaxy.
The second question, of course, was what was producing it. Collisions between cosmic rays and the gas in the interstellar medium are primarily responsible for generating gamma rays in the Milky Way.
The Sagittarius galaxy cannot be created because the smaller satellite galaxy is currently gravitationally falling into the Milky Way, and has been for some time. 2 to 3 billion years ago, the gas was most likely stripped away from this small satellite galaxy.
Furthermore, no significant stars have been dying in extraordinary supernovae; these events are caused by gas, and currently. There is a limited amount.
So what could be causing these gamma rays?
The team investigating the cause of the anomaly came to the conclusion that it was most likely due to millisecond pulsars. These are neutron stars (the collapsed cores of dead massive stars) which spin at an extremely fast rate, on millisecond scales. As they spin, they emit jets of radiation from their poles - including gamma radiation.
The new stars in the Sagittarius galaxy would be compatible with the most recent episodes of star formation and have the same spatial distribution as other existing stars.
If the pulsars are around 7 to 8 billion years old, and low in metal compared to other galaxies, this would be possible- which is consistent with what the researchers discovered about the Sagittarius population. Although gamma radiation from these pulsars seem bright , it's dimmer in comparison to competeing galaxies such as Andromeda.
The researchers say that their findings new "provide strong evidence against the Fermi Bubbles being associated with a past flaring activity of the Galactic center".
It's more likely that other objects or processes are responsible for the gamma rays- such as millisecond pulsars, young and metal-poor stars, or something else entirely.
According to this research, dwarf spheroidal galaxies such as Sagittarius might emit higher levels of gamma radiation than anticipated.
The team says that more observations are needed to better understand the emission mechanisms at play in these galaxies.
This is an interesting development because it helps to rule out one possible source of the gamma rays, but there is still much mystery surrounding their emission.
Dark matter signals, one of which is gamma radiation emitted when dark matter particles and antiparticles annihilate each other, could beconfounded by these objects.
The probability, according to the researchers, should encourage further study of these tiny, faint galaxies to see if our current ideas of dwarf spheroidal galaxies and ancient star populations are accurate.
The research has been published in The Astrophysical Journal.
Billy Carson - The Secrets of the Pleiades: The world's Oldest Cosmic Story
About the Blogger:
April Carson is the daughter of Billy Carson. She received her bachelor's degree in Social Sciences from Jacksonville University, where she was also on the Women's Basketball team. She now has a successful clothing company that specializes in organic baby clothes and other items. Take a look at their most popular fall fashions on bossbabymav.com
To read more of April's blogs, check out her website! She publishes new blogs on a daily basis, including the most helpful mommy advice and baby care tips! Follow on IG @bossbabymav
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