Remove this ad

Did Dark Matter Annihilate Our Early Universe?

by Ian O'Neill on April 26, 2009

Want to stay on top of all the space news? Follow @universetoday on Twitter

A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions.

A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions.

380,000 years after the Big Bang, the Universe cooled from being a hot soup of plasma, to a temperature where protons and electrons could combine to form atoms. This calm period of neutral hydrogen in universal history didn’t last for long however. The neutral hydrogen atoms were ripped apart once more, by a mechanism that would go on to reionize the entire Universe, a process that eventually ended a billion years after the Big Bang.

Remove this ad

It is thought the first stars that formed prior to the reionisation epoch probably pumped out some fierce ultraviolet radiation, ionizing the neutral hydrogen, but a new (controversial) theory has been put forward. Did dark matter have a role to play in the reionisation the Universe?

As 85% of the Universe is composed of a type of matter we have yet to fully account for, it seems only natural that scientists would be looking into the possibility that dark matter had a role to play soon after the Big Bang. Although scientists are fairly confident that the reionisation period was driven by the emissions from the very first stars, there are some observational factors that could suggest dark matter annihilation might have had a role to play in the evolution of the Universe.

This is according to Dan Hooper and Alexander Belikov from Fermilab in Batavia, Illinois, in any case. In their theory recently published, the researchers examine the physics behind dark matter annihilation as the mechanism that drove the reionisation epoch.

reion_diagramIn Hooper and Belikov’s work, they focus on dark matter that is theorized to have clumped together under gravitational attraction as the Universe cooled during the neutral hydrogen era (known as the “Dark Ages” – the Universe would have been opaque due to lack of stars and lack of electromagnetic radiation). When the dark matter during this time clumped, it is predicted to annihilate. During dark matter annihilation, high energy gamma-rays are predicted to be generated. Where gamma-radiation goes, ionization of matter is sure to follow.

“A single gamma ray might reionise 1000 hydrogen atoms,” says Hooper. “The mechanism could easily have reionised the universe.”

By their reasoning, rather than emissions from stars that may have been forming at the start of the reionisation epoch, a far more potent ionization mechanism could have flooded the Universe. However, some scientists are skeptical of this idea.

“We have no evidence yet that any dark matter has ever annihilated,” says Charles Bennett, principal investigator on NASA’s WMAP satellite, which has been studying the reionisation epoch. “I am not saying it is wrong, but it sounds a bit too contrived for me to eagerly accept it.” Bennett sees the dark matter argument as one mystery (reionisation) being explained by another mystery (does dark matter even annihilate?).

For now, the idea that dark matter may have been the underlying mechanism ionizing our Universe remains highly theoretical. But Hooper is eager to study the data from ESA’s upcoming Planck mission as this observatory will be able to study how reionisation proceeded with time. “The time signature of dark matter reionisation will be different from that brought about by stars,” says Hooper.

Source: New Scientist

Remove this ad

About

[Follow me on Twitter (@astroengine)]

[Check out my space blog: Astroengine.com]

[Check out my radio show: Astroengine Live!]

Hello! My name is Ian O'Neill and I've been writing for the Universe Today since December 2007. I am a solar physics doctor, but my space interests are wide-ranging. Since becoming a science writer I have been drawn to the more extreme astrophysics concepts (like black hole dynamics), high energy physics (getting excited about the LHC!) and general space colonization efforts. I am also heavily involved with the Mars Homestead project (run by the Mars Foundation), an international organization to advance our settlement concepts on Mars. I also run my own space physics blog: Astroengine.com, be sure to check it out!

← Older Comments
  • ShadowDancer

    InvaderXan Says:

    I must admit, I have to join the skepticism here somewhat (which is atypical for me!). Surely if we can account for reionisation without needing a dark matter annhilation mechanism (and, to the best of my knowledge, we can) — then isn’t this theory in violation of Occam’s Razor…?

    *****
    Occam’s Razor doesn’t necessarily mean anything. If two competing theories for something have different amounts of assumptions, then generally it is true that the simplest theory is most likely correct. On the other hand, some of those assumptions in the theory with more assumptions could be correct and actually cause that theory to have fewer assumptions than the simpler one (in which case it probably has wrong assumptions). Occam’s Razor is a good place to start for which theory is likelier (assuming that everyone agrees on all of the assumptions) but it doesn’t necessarily mean that one theory is more correct than another. Many theories have become more complex as more knowledge has been learned about a particular subject which would violate Occam’s Razor if you left the new knowledge in the “assumption” category. Only time and further experimentation will decide which is correct.

  • Lawrence B. Crowell

    The neutralino decay is a leptonic channel. I think the idea for hadronic decay is that the CP violating process in leptonic channels is compensated for by the axion. The axion has not been expeirmentally found, though its tiny mass makes it tough to find.

    It should be interesting to see how the DM problem works through in the near future.

  • Jon Hanford

    @ Lawrence B. Crowell: A different group of researchers posted their theoretical work on axions the same day as the previous paper. In “Axions as Dark Matter Particles” and described their ‘Axion Dark Matter eXperiment’ ADMX to look for axions. Their paper is here: http://arxiv.org/PS_cache/arxiv/pdf/0904/0904.3346v1.pdf . While the hunt for axions (or their absence) has been a long one, I think it illustrates just how science is done via theory and experimentation. “It should be interesting to see how the DM problem works through in the near future.” (btw, I’m hoping neutralinos pan out)

  • Olaf

    solrey Says:
    “There are so many contradictions in the standard model it’s ridiculous. One day it’s dark matter this, dark matter that. The next day it’s modifying gravity theory eliminating the need for dark matter all together. The emperors clothes are frayed beyond recognition at this point.”

    Yes so what? This is how science works, theories are created, and the get tested! If a theory fails in it’s test by other cross references using different techniques and means then it just gets disregarded and thrown in the bin.

    Sometimes we get conflicting theories so they will be tested both of them by independend researches and those that fails tests are bad. It could be perfectly possible that both theories are dead wrong!

    You can only test theories by throwing it to the lions (yes other science peorple) trying to schread it to peaces. If it gets schreadded then it did not pass a test. Most alternative theories just gets schredded in the first pass.

    The only reason why some alternative theories gets beeing popped up after beeing schreaded by scientists is because om some theories have become a real religion and some guru’s are trying to impress people with secret knowledge that now one knows so they get these brainless followers that have no clue in understanding what this guru means but it sounds impressive so it must be true.

← Older Comments

Previous post:

Next post: