Mysterious gamma rays may not be emanating from Fermi bubbles after all: science alert

A gamma ray rogue has just been found near the Milky Way.

Active radiation previously associated with structures emanating from the center of the Milky Way is called Fermi bubbles In fact it seems to come from something further.

The assets are instead believed to be milliseconds pulsars In a small dwarf galaxy orbiting our galaxy.

This discovery has implications for our understanding of the Fermi bubbles, but could also have an impact on broader areas of research, such as the search for the galaxy. dark matter.

Fermi bubbles were discovered in 2010, and it was a huge surprise in every sense of the word. They are giant 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, expanding at a rate of millions of miles per hour.

Visualization of Fermi bubbles. (NASA’s Goddard Space Flight Center)

Everything that created them – the enormous Milky Way Black hole Be a leading candidate – he did this millions of years ago, and the bubbles have been blowing up and out ever since. It is much brighter in high-energy gamma radiation than the rest of the Milky Way’s disk.

Not all radiation from Fermi bubbles is evenly distributed. In particular, there is what is described as “cocoon“Recently accelerated cosmic rays in the southern lobe, which were interpreted when they were discovered in 2011 as part of the super-bubble environment.

Now, a team of astronomers, led by astrophysicist Roland Crocker of the Australian National University in Australia, has noticed something interesting.

The location of the cocoon directly corresponds to the location of another object – the core of the Sagittarian dwarf globular galaxy, a satellite of the Milky Way in the process of being torn apart by the larger galaxy.

That, on its own, would be pretty great common toners, with a very small probability of around 1 percent. But it becomes more interesting. The Cocoon and the Sagittarius galaxy also have similar shapes and directions.

Of course, it can be very difficult to measure distance in space. Unless you know exactly how much light something is emitting, it’s hard to know how far away it is.

If you see something emitting gamma radiation in a larger structure of gamma radiation, it is natural to assume that the two are related. But two things of the same shape and orientation lining up directly in our field of view would be really strange.

It’s not impossible, but there might be a more likely explanation – such as a connection between these two objects.

So the researchers decided to revisit the cocoon, and see if the dwarf galaxy could be an alternative explanation for the gamma radiation observed in it.

They modeled the emission across a range of interpretations, including the inner bubble cocoon and the Sagittarius galaxy, and found that the Sagittarius galaxy was probably the most likely emitter of gamma radiation in the Fermi cocoon.

The next question, of course, was what he could produce. In the Milky Way, gamma rays are generated mostly by collisions between cosmic rays and gas in the interstellar medium.

This is not possible for the Sagittarius galaxy. A smaller satellite galaxy gravitationally falls into the Milky Way, and been for some time; As such, its gas was meticulously stripped away, probably about 2 to 3 billion years ago.

Nor have any massive, short-lived stars die in spectacular supernovae. These are born out of gas, and, well. There is no.

The team found that the most likely explanation is millisecond pulsars. These are neutron stars (the very dense collapsed cores of dead massive stars) with extremely fast rotation rates, on millisecond scales; As it rotates, it emits jets of radiation from its poles – Including gamma radiation.

These would be consistent with the latest star-forming episodes in the Sagittarius galaxy, and have the same spatial distribution as the rest of the star groups.

Although gamma radiation appears bright compared to other galaxies such as Andromeda, this would be possible if the pulsars were 7 to 8 billion years old, and low in metal content — consistent with the rest of Sagittarius, the researchers say.

This finding suggests that dwarf spheroidal galaxies such as Sagittarius may be producing more gamma radiation than expected.

If so, this could confuse the search for dark matter signals, which is presumably one of those dark matter signals. increased gamma radiation Emitted as dark matter particles and antiparticles annihilate each other.

The researchers say the possibility should prompt a closer look at these faint little galaxies, to see if we need to revise our understanding of dwarf globular galaxies, and the ancient clusters of stars that contain them.

The search was published in natural astronomy.