Download WIMPs vs. MACHOS: What's the Matter?

THE DARK SIDE OF THE FORCE Black Holes and Dark Matter
Weldon J. Wilson
Department of Physics & Engineering
University of Central Oklahoma
Historically, astronomers have harvested light
Is there material that does not emit or absorb light?
Planets
Comets
Stars
Galaxies
Yes!
Dark Matter
What is it made of?
We don’t know
How much is there?
Most of the Universe!
Particle Physics
Astronomy
Cosmology
How do we know?
“We see it as Columbus saw America from
the shores of Spain. Its movements have
been felt, trembling along the far-reaching
line of our analysis, with a certainty hardly
inferior to that of ocular demonstration”
Sir John Herschel
(referring to evidence for
Neptune, 150 years ago)
Rotation Curves of Spiral Galaxies
NGC 253
Spiral galaxies like our own
Milky Way are rotating.
The rate of rotation can be
measured, and used to
determine the mass of the
galaxy.
(David Malin, AAO)
The stars in a typical galaxy comprise
at most 10% of its mass!
Revised notion of a galaxy
With our Dark Matter glasses on:
A cosmological Rosetta stone?
Dark Matter
• governs the majestic rotation of galaxies
• seeds the evolution of cosmic structures
• determines the fate of the Universe
Understanding the nature and distribution of
Dark Matter is one of the most pressing open
questions in the physical sciences today
The Mass Budget of the Universe
closed
“Critical” density
open
Ordinary
(“Baryonic”)
Matter, at most 10%
of critical density
“Best Guess” Density of
the Universe
Stars, less than 1% of
critical density
What is the Galactic Dark Matter?
Gas,
Dust
Exotic Particles
New Physics!
Ordinary
Matter
Stars
MAssive
Compact
Halo
Objects
Jupiters?
Black Holes?
Brown Dwarfs?
Massive
Neutrinos
??
Axions
Weakly
Interacting
Massive
Particles
Searching for Particle Physics Dark Matter
•
•
•
•
Direct Detection of WIMPs
Direct Detection of Axions
Fossil Record - tracks in mica
Neutrino experiments:
1) Do neutrinos have a non-zero mass?
2) Searches for annihilation decay products
DM + DM
neutrinos
Searching for WIMPs
Experimental Challenges:
low rate
background discrimination
Thermal and ionization
signature in laboratory
apparatus
Deep underground
cryogenic experiment
Is the mass of the neutrino exactly zero?
A new generation of experiments will determine
properties of neutrinos
Sudbury Neutrino
Observatory, Canada
SuperKamiokande, Japan
Scanning for Axions
• Specific prediction relates the axion’s
mass to its interaction rate
• In a strong magnetic field, axions convert to light
sensitive detector
signal
frequency
superconducting magnet
(LLNL/MIT/Florida)
Searching for MACHOs
How do you look for something that can’t be seen?
Use the one thing that is known about Dark Matter:
- It Gravitates!
Telescope
Star
MACHO
Gravitational Lensing
Within the solar system, deflection of light grazing past the
sun provides a stringent test of General Relativity
Over cosmological
distances, lensing by
intervening galaxies
produces dramatic
effects
From a Black Hole Not even
Light Escapes
Gravitational Lensing By a Moving Mass
The Signature of Gravitational Microlensing
star
Brightness
The Signature of Gravitational Microlensing
star
MACHO
speed mass
Brightness
duration depends on
speed and mass of MACHO
peak depends on how close
it passes to line of sight
Gravitational Microlensing by MACHOs
Unlikely!
One star in a million is
lensed at any given
time
you are
here
Distinctive signature is
a brightening of a
background star
Requires a population of stars just outside the Galactic
dark halo, but close enough to monitor individual stars
MACHO Project - lines of sight
you are
here
towards
Galactic
Center
towards Large
Magellanic Cloud
(M65, David Malin, AAO)
The Needle in the Haystack
Single Image
77 Mbytes = 3 Seattle phone books
Typical night
5,000 Mbytes = 200 phone books!
Total to date
5,000 Gbytes = 200,000 phone books
More repeated measurements of stars than the entire
cumulative previous history
of astronomy
The MACHO Project - Data Analysis
Image
77 Mbytes Analysis
per frame
Image
Archive
Database
Time Series Analysis
Alert System
Many stars are variable!
Eclipsing Binary
systems
Periodic variable stars
Exotic stars...
boom!
Eclipsing Binary Star System
Periodic Variable Stars
Microlensing has been detected
• The trick is distinguishing microlensing
from intrinsic stellar variability
• More than 200 events seen towards Galactic
center
• Valuable new tool for astrophysics
days
Amplification
Gravitational Microlensing is Very Useful
• Lensed stars are brighter!
Can get detailed data
• Better detail than Hubble Space Telescope
• Mass tomography of the Galaxy
• Search for distant planets around disk stars
• Search for Dark Matter
Looking for Planets with Microlensing
• Take advantage of hundreds of events
towards Galactic Center
• Planetary companions to lensing stars in
Galactic disk produce excursions in light
curves
• Sensitive to Earth-mass planets
• Preliminary data look encouraging
As for the search for MACHOs...
After looking at more than twenty million
stars for two years - a pair of observations:
• No short events seen.
• A handful of surprisingly long events
detected...
Lack of short events rules out a wide range
of MACHOs being the Dark Matter
excluded
1 million times
less massive than
the sun
one tenth
as massive
as the sun
Eliminating DM candidates is major progress!
A detection of Dark Matter?
Eight microlensing events were seen in a
two-year period, after monitoring twenty
million stars
This significantly exceeds the single
event expected from “known” stars in the
Galaxy
The Puzzle
The detected events last roughly 80
days, corresponding to lenses with
about 1/10th the mass of the sun
What could these things be?
If the preliminary results endure, this
could be a turning point
So, what is the matter?
The least radical option:
– MACHOs and/or massive neutrinos.
More speculative:
– exotic elementary particles never before seen
We live in a special time in
human history
Some of the most fundamental questions in
cosmology are being successfully addressed by
experiments.
The measurements are difficult, with results that
sometimes appear contradictory.
A much more complete understanding will take
shape in the decade to come.
The Future
Next-generation
microlensing projects,
along new lines of sight
Results from
WIMP and Axion
Searches
Neutrino Results
Other observational
cosmology projects