margaret m. hanson, phd associate professor of physics
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Margaret M. Hanson, PhDAssociate Professor of Physics
The Andromeda Galaxy
Our Galaxy’s Globular Clusters
• Reside in Halo• Perhaps 1000s
originally formed• 200 exist today• Contain 100,000
solar like stars• Variety of orbits• Ages greater than
10 billion years
M10 -- Globular Cluster
How do Massive Clusters form?
First, we began to see evidence of very massive clusters (proto-globular clusters) forming in other galaxies
We used to think massive cluster formation to be a thing of the past (the Globular Clusters).
Young Globular Cluster NGC 1850 in the LMC
30 Doradus in the LMC
How do Massive Clusters form?
Massive clusters are seen to form when enormous dynamical stress or collisions occur within galaxies.
Massive clusters can form in relatively recent times. What triggers them to form?
Galaxy Collisions
The Milky Way is colliding, too!
Where would Young Cluster live?
Stars form when gas and dust collapse under its own self gravity.
Gas and dust reside ONLY in the disk of our Galaxy.Young clusters must reside in the disk of our Galaxy.
Studies in our galaxy are not able to see very far in the disk and sample a very small portion of our galaxy.
Luminosity of Disk Star Clusters
Massive stars are rare.
Massive clusters are rare, too.
h & chi Per
Orion
Massive Clusters in our Galaxy
1) HST imaging reveals dense, young, galactic clusters previously unresolved.
Recent events have forced us to re-evaluate the notion of young massive clusters within the Milky Way.
NGC 3603
Massive Clusters in our Galaxy
2) Infrared imaging discovers new, very massive clusters near the galactic center
Recent events have forced us to re-evaluate the notion of young massive clusters within the Milky Way.
Massive Clusters in our Galaxy
3) Deeper imaging of known galactic clusters has revealed a more substantial number of stars.
Recent events have forced us to re-evaluate the notion of young massive clusters within the Milky Way.
Westerland 1 and its massive stars
Even nearby we are uncertain!
The Cyg OB2 Cluster
Distance = 1.7 kpc
60 massive stars identified.
Knoedlseder (2000) found the Infrared Cluster to be ‘rounder’ and containing more stars than the Optical Cluster.
Contours of stellar counts
Why the difference? Dust!
CO intensitymap
The interstellar matter (gas and dust) forces us to observe at longer wavelengths.
Are there super massive star clusters in our Galaxy?
Westerlund 1: D = 3-5 kpc, Av= 11, >100 O stars. Consistent with being “one of the most massive young clusters in the Local Group”.
Cygnus OB2: ~100 O stars, D = 1.7 kpc, Av = 5-10
Infrared Surveys: have found > 50 new galactic star clusters in the inner galaxy.
We will need to move ALL observations and analyses to the infrared.
Spectra of Hot Stars at 2 microns
45,000 KO3-O4
42,000 KO5-O6
40,000 KO7-O8
36,000 KO9-B0
29,000 KB1-B2
He I2.058 He I 2.11
C IV N III
Br Gamma
He II
Observing time granted
8.2m VLT with ISAAC.
2 nights March 2000
2 nights June 2000.
2 nights June 2001
8.2m Subaru with IRCS.
2 nights November 2001
2 nights June 2002.
• Develop quantitative methods for the analysis
of massive stars and massive clusters relying on infrared light only.
• Continue to search for clusters deep within the Milky Way galaxy using infrared imaging.
• Ultimate goal: uncover the massive clusters and the hidden structure of the Milky Way.
Future Research Goals