Download A Tale of Star and Planet Formation

A Tale of
Star and Planet
Formation
Lynne Hillenbrand
Caltech
Vermeer’s
The
Astronomer
(1688)
Mauna Kea
(last week)
photos by: Sarah Anderson and Bill Bates
Context: Our Sun
• The Sun is a completely average star.
– typical weight
– middle age
SOHO satellite
Context: The stars
• At first consideration it
might seem as though
the Sun and other stars
are constant and
unchanging.
• However, stars are born,
they live, and they die.
• Many are forming today
throughout the Milky
Way (3 MSun per year).
2MASS
Star formation in galaxies
Milky Way galaxy
M51 galaxy (central region)
HST
The Solar Neighborhood
Warm interstellar gas
(low density)
Cold gas clouds (dense)
Young clusters
Ionized gas (HII region)
from massive star winds
& supernovae
[Huff & Frisch]
450 pc
1500 Lt yrs
Where do Stars Form?
Molecular gas ( CSO )
Optical image ( HST )
Light comes in different “Wavelengths”
slide courtesy of A. Goodman
Astronomical dust
Wavelength vs Particle Size
“Dust
Grain”
“Dust
Grain”
Light is “Extincted”;
Does not Reach Us
Light Goes Right by;
Reaches Us
Scatterer
Light “Scatters”
Blue: 3.6 μm
Green: 4.5 μm
Red: 8.0 μm
slide courtesy of T. Megeath
Perseus-Taurus-Orion
optical photograph (star light)
mid-infrared (dust emission)
Orion in visible and infrared light
Zooming in on Orion
Akira Fujii
David Malin
HST image
Bob O’Dell
“Nebula” is created by reflected light from hot, massive stars
Keck Studies of Newborn Stars
• imaging photometry
• spectroscopy
Slesnick, Hillenbrand, Carpenter
MWC 1080
M1
M3
B0
K1
M2
M4
K7
Where do
stars form?
• Cold clouds of atoms,
gas molecules, and dust
having masses a few
hundred to a few million
times the mass of the Sun.
factor of 1 million in density
factor of 1 million in density
Compress yet another factor of 1 million x 1 million to get a star!
How do Stars Form?
80,000 AU and 250,000 years
Why do stars form?
Local Star Formation
[North American / Pelican Nebulae]
2MASS
Stars Tend to Form
in Groups, not Alone
Aggregates (unbound)
• 10’s of stars
• 0.4 - 1.6 lightyear radius
• <100 stars / unit volume
Clusters (may be bound)
• 100’s to 1000’s of stars
• 1.6 - 16 lightyear radius
• 1000 - 100,000 stars / volume
2MASS
1 parsec is the
distance at
which Earth
would appear
1” away from
the Sun (about
3.3 light years)
Note that the
distance to our
nearest
neighboring
star Centauri
is ~1.3 pc
Binary Stars
Our Sun is a single
star, but half of all
Sun-like stars are
found to be in
multiple systems
(twins, triplets,
quads).
Models of star
formation have
trouble predicting
exactly how these
systems are made.
We are using Keck to observe young binary
systems as they form. These studies are difficult
because binary stars are typically very close
together in projection and because atmospheric
distortions blur our observations.
Keck can observe these stars because of a
technology called Adaptive Optics. AO corrects the
atmospheric distortions that normally limit the
resolution of telescopes.
In typical 0.8” astronomical
seeing, a telescope on
Mauna Kea can separate the
two headlights of a car on
Haleakala. Keck + AO could
do this for a car in Los
Angeles!
Adaptive Optics
without AO
0.80” seeing
(FWHM)
with AO
FWHM=0.09”
• Eliminates atmospheric turbulence;
• Allows high-contrast imaging (106).
Binary star HD 18940
with the Palomar AO system
Very young binary
systems look very similar
to the old stars that are
our nearest neighbors.
This means binaries
probably form this way,
V410 X-ray3
instead of being
influenced by close
encounters with other
stars in their cluster/family.
HST (0.8 um)
0.05”
7 AU
vs
Keck (1.6 um)
“diffraction limit”
=
wavelength
------------------------telescope diameter
IZ-072
How Do Young Stars Form?
The cloud contracts, and
collapses to create a protostar.
Leftover gas and dust flattens
into a disk.
A significant amount of this gas
and dust spirals into the star
(“accretion”).
Some dust in the disk can collide
and stick together (“grain
growth”). Eventually, pebbles,
asteroids, and rocky planets as
well as giant planet cores can
form.
Star and planet formation
10
105 yr
Disk/wind
Lstar
104 yr
Planet building
107 yr
109 yr
1
Planetary system
100 AU
Main
sequ
ence
8,000
5,000
Cloud collapse
2,000
Tstar (K)
[Beckwith & Sargent 1996]
With Keck we are studying:
•
•
•
•
•
•
•
Young stellar populations (how big? how old?)
Clustering and multiplicity (families)
Outflow of material in winds and jets
Accretion of material onto forming stars
Geometry of circumstellar disks
Dissipation of disks and planet formation
Discovery of planets around more mature stars
Collaborators on Keck work:
Scattered light from Protostars
Protostellar Outflows
• Remove angular momentum
• Generate turbulence in molecular cloud
Evidence for Outflows
Edwards et al 06
“Blue side” absorption in He I at 1.083 μm:
broad = stellar wind (seen in strong accretors)
narrow = disk wind (seen in weak accretors)
[Matt & Pudritz 2005]
Evidence for Accretion
accreting young stars
normal young stars
The Inner Accretion Disk
• Origin of outflows.
• Nature of accretion
flows that shock and
heat photosphere.
[Hartmann 1998]
• How big are the
indirectly inferred inner
disk gaps?
Interferometry
• Direct imaging is limited by the
“diffraction limit” or (wavelength/diameter).
This is 0.013-0.045” for a 10m telescope
operating in optical/near-infrared. requires AO
• We can be even more clever! gets to 0.0048”
slide courtesy of J. Eisner
Lambda
Building Planets from the Raw
Materials in Circumstellar Disks
• Dust evolution:
– growth from interstellar medium sized dust to larger solids:
μm cm km moon/Mars sized “oligarchs” 1-10 Mearth planets
• Gas dissipation:
•
•
•
•
accretion on to star
outflow in winds/jets
irradiation
formation of planets
[animation by Jeff Alu]
How do Planets Form?
Formation of Other Solar Systems
• “Proto-planetary” disks
– Exist around all stars younger than a
few million years (<1/1000 Sun’s age)
– Disappear on time scales of less than
10 million years
• Need to turn dust and gas into
planets before the disk disappears!
The view from a newborn planet
History of Exo-Solar System
Planet Detection
Planets now
suspected to
orbit ~8-15% of
solar type stars
in the solar
neighborhood,
with many
multiple planet
systems known.
Planetary Masses from Keck RVs
TrES-2
TrES-1
1.28 MJup
0.75 MJup
TrES-3
1.92 MJup
TrES-4
0.84 MJup
Search for Exoplanets using Transits
TrES-2 Photometry
Bright
Star
Dark
Planet
2
r rp p
F = = 1%
R RJup 2
RSun R 2