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 M Sun 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? Optical image ( HST ) Molecular gas ( CSO )
Light comes in different Wavelengths slide courtesy of A. Goodman
Astronomical dust
Wavelength vs Particle Size Dust Grain Light is Extincted ; Does not Reach Us Dust Grain 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
M1 MWC 1080 M3 K1 B0 M4 K7 M2
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 ( 10 6 ). 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, instead of being V410 X-ray3 influenced by close encounters with other stars in their cluster/family. 0.05 7 AU HST (0.8 um) 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 Disk/wind 10 5 yr L star Planet building 10 4 yr 1 10 9 yr Planetary system 100 AU 10 7 yr Main sequence Cloud collapse 8,000 5,000 T star (K) 2,000 [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: [Matt & Pudritz 2005] broad = stellar wind (seen in strong accretors) narrow = disk wind (seen in weak accretors)
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. We can be even more clever! requires AO 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 M earth 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-1 TrES-2 0.75 M Jup 1.28 M Jup TrES-3 TrES-4 1.92 M Jup 0.84 M Jup
Search for Exoplanets using Transits TrES-2 Photometry Dark Planet Bright Star F = r p R 2 =1% r p R Jup 2 RSun R 2