cosmology and extragalactic astronomy mat page mullard space science lab, ucl 6. dark matter
TRANSCRIPT
![Page 1: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/1.jpg)
Cosmology and extragalactic astronomy
Mat Page
Mullard Space Science Lab, UCL
6. Dark matter
![Page 2: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/2.jpg)
5. Dark Matter
• This lecture:• Dark Matter:
– where is it?– what could it be?– some experiments to find it.
Slide 2
![Page 3: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/3.jpg)
Recap of galaxy rotation
• Orbital velocities rise OK but then don’t fall off.
• Something wrong– Either gravity not 1/r2 (!!)– or there is more mass than we can see.– This is “dark matter”
Slide 3
![Page 4: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/4.jpg)
Slide 4
![Page 5: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/5.jpg)
Where must the mass be?
• Recall M = r v2/G
• If M varies with radius, and v is constant
• Mass proportional to radius
• for a disc thickness h, density
• for a sphere, density
• Must extend out to visible edge of galaxy
= 3v2
4Gr2
= v2
Ghr
Slide 5
![Page 6: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/6.jpg)
• Two classes of candidates:• MACHOs
– Massive Compact Halo Obects
• WIMPs– Weakly Interacting Massive Particles
What could dark matter be?Slide 6
![Page 7: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/7.jpg)
• Discrete objects that are very difficult to detect:– Brown dwarfs / large Jupiters– White dwarfs– Small black holes.
What could MACHOs be?Slide 7
![Page 8: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/8.jpg)
• New particles we haven’t yet seen: – Neutrinos– Lightest Supersymmetric particles
(neutralinos)– Axions (Big bang remnants).
What could WIMPs be?Slide 8
![Page 9: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/9.jpg)
Detecting MACHOs
• Machos are small and dense.
• But they have mass, so cause curvature in spacetime.
• Will focus light from a background star as they pass in front - star will change brightness.
Slide 9
![Page 10: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/10.jpg)
MACHO events
• MACHO project looked for these events.• 1m telescope in Australia looked at LMC every
night possible for several years.• Saw some!
Slide 10
![Page 11: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/11.jpg)
..but not many
• Not many low-mass (planet size) MACHOs.
• Some 0.5 Mo events (black holes, white dwarfs?)
• MACHOs could account for UP TO 40% of dark matter.
Slide 11
![Page 12: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/12.jpg)
Detecting WIMPs
• Several current + future experiments
• This is a NaIAD detector from UKDMC, Boulby Mine
• Look for recoil from “Heavy WIMP”
• None confirmed yet.
Slide 12
![Page 13: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/13.jpg)
How are they doing?
UKDM
Other planned experiments
Slide 13
![Page 14: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/14.jpg)
But none found so far
• Big, risky science.• Would be as important for particle
physics as for cosmology.• Could net the Nobel prize if found.• But you have to detect one first.
Slide 14
![Page 15: Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL 6. Dark matter](https://reader035.vdocument.in/reader035/viewer/2022070306/5515dc18550346cf6f8b4ad6/html5/thumbnails/15.jpg)
Some key points about dark matter:
• 90% of the mass in the Universe• Most of the mass in the outer parts of galaxies.• Two possible candidates for dark matter:• WIMPs
– weakly interacting massive particles– searches underway, none found so far
• MACHOs– massive compact halo objects– can only make up to 40% of dark matter
Slide 15