What is Hot Dark Matter theory?
I have heard of something called HDM which is a theory to explain dark matter that is no longer as popular as it used to be. What is HDM?
Two theories to explain the composition of dark matter are Hot Dark Matter theory (HDM) and Cold Dark Matter theory (CDM). The main difference between the two theories is the speed of the candidate particles. As you may have guessed, HDM particles move quickly (and are thus “hot”) while CDM particles move slowly. Neutrinos are the main HDM candidate for dark matter as they are very weakly interacting and exist in such large numbers in the universe.
The main problem with HDM theory is that the high speeds of the particles (i.e. neutrinos) in the early universe could not have allowed small density fluctuations to clump together in order to create the large fluctuations we see now. We believe matter (or in other words galaxies) is distributed throughout the universe as it is now due to the growth of small initial fluctuations. Since neutrinos would have been moving so fast that these tiny initial fluctuations would have been smoothed out, HDM theory cannot account for the distribution of galaxies in the universe. The small scale of this initial clumping that is impossible for neutrinos to maintain is supported by COBE observations.
Now when HDM is discussed, it is usually in combination with CDM (the combination is called MDM or “mixed dark matter”). HDM is thought to be limited to at most a few percent of dark matter if the amount is even measurable.
Get More 'Curious?' with Our New PODCAST:
- Podcast? Subscribe? Tell me about the Ask an Astronomer Podcast
- Subscribe to our Podcast | Listen to our current Episode
- Cool! But I can't now. Send me a quick reminder now for later.
How to ask a question:
If you have a follow-up question concerning the above subject, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.Table 'curious.Referrers' doesn't existTable 'curious.Referrers' doesn't exist
This page has been accessed 17097 times since February 26, 2006.
Last modified: February 26, 2006 5:29:28 PM
Ask an Astronomer is hosted by the Astronomy Department at Cornell University and is produced with PHP and MySQL.
Warning: Your browser is misbehaving! This page might look ugly. (Details)