(ORDO NEWS) — Something deep in the heart of the Milky Way galaxy is glowing with gamma rays, and no one can pinpoint exactly what it might be.
A dark matter collision was proposed, ruled out, and then tentatively revised.
Dense, rapidly spinning objects called pulsars were also considered sources of high-energy radiation, but were then dismissed as too few for the sums to add up.
A study by scientists in Australia, New Zealand and Japan could breathe new life into the explanation of pulsars by showing how you can squeeze some seriously intense sunlight out of a population of spinning stars without breaking any rules.
Gamma rays are not quite the usual shade of sunlight. Its production requires some of the most energetic processes in the universe. We are talking about the collision of black holes, the acceleration of matter to the speed of light, the connection of antimatter with matter.
Of course, the center of the Milky Way has all this in abundance. So when we look at the sky and consider all these collisions of matter, spiraling black holes, pulsars and other astrophysical processes, we expect to see a healthy gamma-ray glow.
But when ten years ago, researchers using NASA’s Fermi Telescope measured the intense aurora at the heart of our galaxy, they found that there was more of this high-energy light than they could explain: a phenomenon known as galactic center excess.
One interesting possibility has to do with invisible pieces of matter colliding with each other in the night. These weakly interacting massive particles – a hypothetical category of dark matter commonly referred to as WIMPs – cancel each other out when they collide, leaving nothing but radiation to signify their presence.
This is a funny explanation, but it also does not require proof.
“The nature of dark matter is completely unknown, so any potential clues are of great interest,” says astrophysicist Roland Crocker of the Australian National University.
“But our results point to another important source of gamma-ray production.”
This source is a millisecond pulsar.
To create it, you need to take a star much larger than ours and let its fire die out. In the end, it will turn into a dense ball no wider than a city, where atoms are so tightly packed together that many protons slowly turn into neutrons.
This process generates super-strong magnetic fields that direct incoming particles into fast-flowing streams that glow with radiation.
As the object rotates, these currents rotate around the star’s poles like the largest beacons in the universe, so the star appears to be pulsing with energy. Pulsating stars rotating hundreds of times per second are known as millisecond pulsars, and we know a lot about the conditions under which they could form.
“Scientists have previously detected gamma rays from individual millisecond pulsars in the vicinity of the solar system, so we know that these objects emit gamma rays,” says Crocker.
However, in order to radiate them, they need a large amount of mass on which they can feed. Most of the pulsar systems at the center of the Milky Way are thought to be too small to emit anything more energetic than X-rays.
However, this is not always the case, especially if the dead stars from which they originated belong to a certain type of supermassive white dwarfs.
If enough of these heavyweights turn into pulsars and keep their binary cycle partners, Crocker says, they will provide just the amount of gamma radiation consistent with observations.
“Our model shows that the integrated radiation from an entire population of about 100,000 such stars would give a signal that is fully consistent with the elevation of the galactic center,” says Crocker.
Being a purely theoretical model, this idea now needs a generous dose of empirical evidence. However, unlike the assumptions based on dark matter, we already know exactly what to look for.”
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