How to get an interesting day:
This is for you that hadn't the chance to participate at the seminar, a very brief overview.
At the end you find links with PDF files with deeper information.
Star formation and star clusters is interesting, how can globular clusters be so old ?
Why are they not disappear by time ?
Some useful links:
Star clusters as footprints of star formation, stellar feedback and assembly history of galaxies:
By PHD Angela Adamo
You can read her abstract here:
"Star clusters are gravitationally bound stellar systems commonly formed in star formation events.
These systems form in the densest regions of giant molecular clouds and host the majority
of the massive stars forming in these regions.
A quick look at the cluster population in our Milky Way already proves that these bound stellar
systems have continuously formed during the assembly history of our own galaxy,
as witnessed by globular clusters, open clusters, young star clusters.
will present some key results that relates the most recent efforts to link the statistical properties
of cluster populations in local galaxies
(i.e. mass functions, dissolution time scales, formation efficiency) to the global physical properties of galaxies,
such has star formation per unit area, gas surface density, and dynamics.
I will show how key events for galaxy evolution, such as mergers or increased gas fraction change the properties
of the stellar clusters formed during these enhanced star formation events,
therefore making them tracers of the assembly history of galaxies.
I will conclude presenting some preliminary results about the effect of cluster feedback on their immediate surroundings and at galactic scales
showing that star clusters are fundamental components of the star formation cycle of galaxies."
Angela has a PhD and has been at Max Planck Institute in Germany before she came to Stockholm University,
the seminar was held at Stockholm University 2019.
From our own galaxy, Milky way we learned about Giant Molecular Clouds (GMC):
- Extended, about 100 pc and marginally stable
- Densities of 102 to 104 particles per cm3
- Supported by turbulence against collapse
1 pc = 3.26 light years, a distance.
Ionising and removing the gas. Stellar feedback -> massive (> 8 MSun) and short lived (< 3-4 million year) stars.
- UV radiation: radiation pressure + photoionization (< 3-4 million year)
- Stellar winds: mechanical energy, shocks, metal enrichment (< 3-4 million years)
- Supernova Explosions: mechanical energy, shocks metal enrichment (4-40 million years)
8 MSun = 8 million times the mass of our Sun.
From Milky way we know that open clusters have ages of about 100 million years and masses of 103 MSun,
globular clusters ages of about 11 billion years and masses of 6x105 MSun.
Our local Universe:
Sometimes it's easier to study star cluster in nearby galaxies from outside. In our own galaxy we see from inside out and a lot of them are hidden behind gas and dust.
Far away galaxies are weak and we need to use gravitational lenses to get signal strong enough.
Because the light speed is not infinite far away galaxies we look at are much younger, example,
a galaxy 1 billion light years away are also how it looked 1 billion years ago.
A time machine that we can use.
There is a difference of star forming activity across cosmic time.
Cluster (ed) Star formation:
- It is not a spacial / rare event
- It is not disconnected from the galactic environment
- It is not confirmed to a specefic period of the cosmic formation history