5 ms·

I have a noob question. How do astronomers know that the stuff they don't see is this exotic "dark matter" rather than just regular matter that their telescopes

I have a noob question. How do astronomers know that the stuff they don't see is this exotic "dark matter" rather than just regular matter that their telescopes can't see?

cozzyd 9y ago
Microlensing excludes large unseen objects and the CMB power spectrum suggests most matter is nonbaryonic.
- crimsonalucard 9y ago
  Hi just curious. What is nonbaryonic matter and what is the CMB power spectrum? Also doesn't microlensing involve gravity? Thus the effects of dark matter on microlensing would be identical to regular unseen matter which also interacts with gravity in the same way? What's the difference?
  - cozzyd 9y ago
    The CMB is the cosmic microwave background, essentially the earliest light in the universe from when atoms are formed. The power spectrum of the temperature fluctuations in the CMB contains information about the constituents of the universe because each constituent (radiation, baryonic matter, non-baryonic matter) behaves differently in the early universe. Here is a Scientific American article that offers some explanation: http://background.uchicago.edu/~whu/SciAm/sym1.html http://background.uchicago.edu/~whu/SciAm/sym1.html Microlensing involves gravity. The difference is that normal matter that could be dark matter would be relatively things massive but compact things like black holes and brown dwarfs as opposed to a diffuse halo. The compactness would make them detectable by lensing.
kevinwang 9y ago
What's the difference between the two things you described? To my understanding, the two options you gave are the same: Dark matter is a hypothesized form of matter which does not interact with normal matter or light (i.e. It can't be seen).
- crimsonalucard 9y ago
  Right I'm not questioning the differences between the two. I'm questioning how we know that the unseen stuff out there is regular matter vs Dark matter. Both matter and dark matter can appear dark when not interacting with light or glowing. According to my knowledge dark matter is identified through its gravitational properties. Matter and dark matter both are gravitational hence my curiosity on why we're identifying this unaccounted gravitational effect as "dark matter" rather than regular matter.
  - arduinomancer 9y ago
    Because you can have dark matter in a hot gas cluster which means it should heat up and be observable by its radiation spectrum. Also note dark matter isn’t black like normal matter in the absence of light. It’s literally transparent because it doesn’t interact with light.

I have a noob question. How do astronomers know that the stuff they don't see is this exotic "dark matter" rather than just regular matter that their telescopes can't see?

cozzyd 9y ago

Microlensing excludes large unseen objects and the CMB power spectrum suggests most matter is nonbaryonic.

crimsonalucard 9y ago
Hi just curious. What is nonbaryonic matter and what is the CMB power spectrum? Also doesn't microlensing involve gravity? Thus the effects of dark matter on microlensing would be identical to regular unseen matter which also interacts with gravity in the same way? What's the difference?
- cozzyd 9y ago
  The CMB is the cosmic microwave background, essentially the earliest light in the universe from when atoms are formed. The power spectrum of the temperature fluctuations in the CMB contains information about the constituents of the universe because each constituent (radiation, baryonic matter, non-baryonic matter) behaves differently in the early universe. Here is a Scientific American article that offers some explanation: http://background.uchicago.edu/~whu/SciAm/sym1.html http://background.uchicago.edu/~whu/SciAm/sym1.html Microlensing involves gravity. The difference is that normal matter that could be dark matter would be relatively things massive but compact things like black holes and brown dwarfs as opposed to a diffuse halo. The compactness would make them detectable by lensing.

kevinwang 9y ago

What's the difference between the two things you described? To my understanding, the two options you gave are the same: Dark matter is a hypothesized form of matter which does not interact with normal matter or light (i.e. It can't be seen).

crimsonalucard 9y ago
Right I'm not questioning the differences between the two. I'm questioning how we know that the unseen stuff out there is regular matter vs Dark matter. Both matter and dark matter can appear dark when not interacting with light or glowing. According to my knowledge dark matter is identified through its gravitational properties. Matter and dark matter both are gravitational hence my curiosity on why we're identifying this unaccounted gravitational effect as "dark matter" rather than regular matter.
- arduinomancer 9y ago
  Because you can have dark matter in a hot gas cluster which means it should heat up and be observable by its radiation spectrum. Also note dark matter isn’t black like normal matter in the absence of light. It’s literally transparent because it doesn’t interact with light.