Download Universe of Learning Science Briefing: Our Home, the Milky Way

Our Home, the Milky Way Galaxy
Dr. Sean Carey (IPAC)
Dr. Dan Patnaude (CfA)
Dr. Jessie Christiansen (IPAC)
Dr. Seth Digel (SLAC)
Universe of Learning science briefing
1
August 25, 2016
Planets and Moons
2
Stars
3
Gas and Dust
4
Black Hole
5
Star Formation and the Structure of
the Milky Way
Sean Carey (IPAC/Caltech)
6
6
Structure of Galaxies
M51
Andromeda
M83
IC 2006
LMC
Arp 220
Galaxies show a wide range of shapes
based on their history and environment
NGC 1300
Images courtesy ESA and STScI
7
Our View of the Milky Way
Death Valley / NPS
The Sun is in the midplane of
our Galaxy about 1/3rd of the
distance out from the center,
but what does our Galaxy really
look like?
ISS / NASA
88
Being in the Galaxy is a Tough Vantage Point
Side View from roof of Spitzer
Science Center looking towards
Rose Bowl
Rose Bowl
Aerial View of
Pasadena –
courtesy of
Google Maps
Spitzer Science Center
9
And then there is Dust!
Interstellar dust absorbs and scatters
light just like smog in LA
Donovan
Blue
Red
Infrared
Blue/Red/Infrared
Redder light is blocked less: You can see through most of the
murk in the infrared
10
Going from 2d to 3d : Turning Pictures
into a Galactic Map
There are no rulers that can be observed in our Galaxy.
But there are types of stars called Red Clump Giants for
which we know the intrinsic brightness. They are also
fairly common and bright and can be used to trace the
structure of the Galaxy.
These can be used to measure distances; stars twice as
far away are four times fainter.
A portion of a Spitzer Space Telescope Map of the plane of our Galaxy
11
The Milky Way
Our Galaxy is thought to be a barred spiral galaxy; the shape of the
12
Galaxy on the other side is not really well known
Stellar Birth and Citizen Science
https://www.milkywayproject.org/
http://www.spitzer.caltech.edu/glimpse360
Newly forming stars heat up the surrounding gas and dust that they
form out of, causing the dust to glow brightly in the infrared
13
Stellar Old Age (and Death)… and
Citizen Science
Aging and
dying stars
throw off
shells of
gas and
dust that
glow in the
infrared
Infrared images of shells from the
Spitzer Space Telescope
14
Summary and Future
•
Mapping of our Galaxy in the infrared using the Spitzer Space Telescope (and the
Herschel Space Telescope) has informed us about the structure of our Galaxy and
the lifecycle of stars (in particular how they form and what happens when they die)
•
The maps of our Galaxy answer many questions in NASA’s Cosmic Origins program
•
Future studies of star formation will be conducted with the James Webb Telescope
which will provide a more detailed view of the process
•
Future mapping of the structure of our Galaxy will be done by WFIRST which will
make the first stellar map of the far side of the Galaxy
•
All of these programs have greatly benefitted from citizen scientists who have made
many discoveries by examining the large maps of the Galactic plane produced with
Spitzer
A snake-like shaped region where stars are forming
15
Supernovae and Supernova
Remnants
Dan Patnaude
Harvard-Smithsonian Center for Astrophysics
16
Credit: NASA/CXC
- lifecycles of stars
17
- lifecycles of stars
18
- Example Supernova: SN 1987A
After
Before
19
- the electromagnetic spectrum
20
- the structure of supernovae and their remnants
Credit: Dan Patnaude (Harvard-Smithsonian Center for Astrophysics)
21
- the structure of supernovae and their remnants
Credit: Pat Slane (CXC/Smithsonian)
22
- Example Supernova Remnant: Kepler’s SNR (SN 1604)
Credit: NASA/CXC
23
- Example Supernova Remnant: Cassiopeia A
Credit: NASA/CXC
24
- Example Supernova Remnant: Cassiopeia A - viewed in hard X-rays
Credit: NASA/NuSTAR/CalTech
25
Summary
• Supernova represent the violent endpoints in the evolution of some stars
- they are responsible for the formation of heavy elements, and in
particular the bulk of the metals that we observe in the universe
- some supernova remnants are responsible for accelerating particles up
to very high energies. We see evidence for this in the acceleration of
electrons by highly amplified magnetic fields found in supernova shocks
- by combining data from several NASA missions such as Chandra and
NuSTAR, we are able to test theories for the evolution of massive stars as
well as theories for the synthesis of heavy elements in supernova
explosions, thus addressing fundamental questions posed by NASA in
relation to how the universe works
26
EXOPLANETS
Image credit: NASA/JPL
Jessie Christiansen, NASA Exoplanet Science Institute
27
What are exoplanets?
Artist’s rendering: NASA. Orbits not to scale.
28
How do we find them?
NASA
NASA
Planets pull on their host stars
… this tells us their mass
Planets block the light from their host stars
… this tells us their size
In the last 21 years we have found over 3370
exoplanets!
29
What have we found?
NASA/IAU
30
So many surprises…
A planet where it rains liquid glass...
Planets orbiting two – or even three! – stars...
An egg-shaped planet, distorted by its host star...
Orphaned planets, floating free in interstellar space…
Planets being disintegrated by their host stars...
Newborn planets only a few million years old...
But no Earth twins... Yet!
31
Where are we finding them?
(http://eyes.jpl.nasa.gov/eyes-on-exoplanets.html)
32
How common are planets?
1
3
of stars like the Sun have planets
33
The Milky Way is Full of Exoplanets!
Studying exoplanets helps us to answer many of humanity’s, and NASA’s, biggest questions
How did we get here?
Are we Alone?
NASA
34
Center of the Milky Way
Optical photomosaic (A. Mellinger)
Studying the Galactic Center outside the
visible spectrum
Seth Digel (KIPAC/SLAC)
Universe of Learning Briefing
25 August 2016
35
Finding the Galactic Center
To Earth
Until the 1950s the accepted
location of the GC was off by
>30 degrees!
Radio astronomy allowed
mapping of interstellar gas
dynamics
The direction of the GC is now
known extremely precisely:
Sagittarius A*
Rougoor & Oort (1959)
36
Sagittarius A* is a Massive Black Hole
Keck Near Infrared Observations of
Stellar Orbits around Sgr A*
Tracking motions of
individual massive stars in
orbit around it has allowed
its mass to be estimated
(~4 million solar masses)
Implied density confirms
its black hole nature
~0.1 light year
37
Active Galactic Nuclei
So-called active galaxies have intense,
variable, ‘non-thermal’ emission
Composite image of Centaurus A
Active Galaxy
associated with accretion disks of
matter around their central black
holes
Depending on the wavelength and
direction, this nuclear emission can
dominate the output of the entire
galaxy
A related phenomenon is nuclear jets
of high-energy particles
Centaurus A is a relatively nearby
example
ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al.
(Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)
38
Milky Way is a Sort-of Active Galaxy
A weak jet interacting with ionized gas in the inner few light years
VLA radio observations
Chandra X-ray observations
Jet feature is
~3 light years long
Li et al. (2013)
But the Milky Way may have been more active in the past…
39
The Big Picture at High Energies
Fermi Large Area Telescope
Map of the entire sky at energies >1 billion times visible light
~100 deg across
(thousands of light years)
Glow along the Galactic plane is from cosmic-ray collisions with interstellar gas
The giant lobes above and below the Galactic center were entirely unexpected
Known as the ‘Fermi Bubbles’
May be evidence of previous intense nuclear activity in the Milky Way
40
Other Gamma-Ray Signals from the
Galactic Center: Dark Matter?
On a smaller angular scale
and at lower energies, the
central part of the Milky
Way is glowing more
brightly than expected
One possibility is that this
is indirect evidence for
particle dark matter
The energy distribution of
gamma rays suggests a
particle mass of about 30x
the mass of the proton
Excess Gamma Rays from the Galactic Center region
(at energies 100-300 million times visible light)
~20 degrees
Daylan et al. (2016)
But…
41
Gamma-ray excess: Dark Matter or Not?
Pros
Cons
The Milky Way (and all galaxies) have
several times more mass than can be
accounted for by stars and gas
The implied annihilation rate is in
tension with limits from dwarf galaxy
satellites of the Milky Way
The dark matter is so far known only
from its gravitational effects
The central Milky Way should
contain a large, broadly distributed
population of millisecond pulsars
One plausible theory is that it is socalled WIMPs that do not interact
with light (of course) but can
annihilate each other
Gamma rays from the resulting
particle cascades would be observed
where dark matter is concentrated,
such as the center of the Milky Way
Millisecond pulsars are gamma-ray
sources
At the distance of the Galactic center
Fermi could not detect them
individually, just a glow from their
overall distribution
42
Summary
• Starting ~60 years ago observations outside the visible range opened up the
possibility to find and study the Galactic Center
• This has been advanced by NASA missions for infrared, X-rays and gamma rays
and by ground-based radio and near-infrared observatories
• Sgr A* has been found to be a massive black hole powering a (currently) weakly
active galaxy
• In gamma rays, study of the Galactic center is also motivated by the search for new
particle physics, indirect detection of dark matter
• This is a very active area of research and requires understanding still more
about the center of the Milky Way
• The work described here is within NASA’s
Physics of the Cosmos objective
in the category of How does the universe work?
43
Future Studies
TESS
2017-2018
JWST
2018
Mid-2020s
44
Additional Resources
http://nasawavelength.org/list/1497
Thank you to our presenters!
45