Insights into early stars

14 October 2014

Interview with

Sanchayeeta Borthakur, Johns Hopkins

When we look at very distant clusters of stars in ancient galaxies "far far away" across NGC 6744the Universe we can see light coming from them which has been travelling for literally billions of years to reach us. But theories of how the Universe - and the first galaxies - actually formed suggest that these stars should be cloaked in dense clouds of gas, which should have soaked up the light, blocking its path. So how did this light nonetheless escape to still reach us?

Well, a younger, much closer galaxy might hold the key to solving the mystery. It's very compact and rapidly forming new stars that are - relatively speaking - also very close together. This produces a powerful wind that can literally blow holes in the gas, allowing light to escape. And because we think this galaxy bears a very close resemblance to the earliest galaxies in the Universe, this could explain why we can see them too.

Johns Hopkins astrophysicist Sanchayeeta Borthakur explains...

Sanchayeeta -  Our discovery is that we found ionising radiations.  So that is the radiation that can ionise hydrogen, escape out of this galaxy.  And this is basically important because it provides a viable and very likely scenario for how the young stars in the very early universe were able to get their ionising photons out.

Kat -  This galaxy that you've study, how far away is it?

Sanchayeeta -  Well, this is a nearby galaxy and it is just 3 billion light-years away.

Kat -  That still seems quite far away to me.

Sanchayeeta -  Well in astrophysical terms, it's just like looking something really nearby.

Kat -  Paint me a picture of this galaxy.  What's it like and what makes it able to give out this high energy?

Sanchayeeta -  So, this is a special galaxy in the sense that it is forming a lot of stars.  But more than that, it is forming all the stars in a very compact region.  Say, this producing about 50 solar masses of stars every year.  It has a billion solar masses of stars in about 300 light-years.  And because of that, the combined effect of all the young stars, they generate winds.  The winds together are so powerful that they can sort of blow out parts of the clouds, create these gaps and then through these gaps, the ionising photons really stream out of the galaxy.

Kat -  I guess it's a bit like when you look up at the sky and it's a sunny day, but there are clouds, and you see the sunlight streaming through the clouds.  Is it that kind of effect?

Sanchayeeta -  Yes, it's exactly that kind of effect.  Or rather on a cloudy day, only through the parts of the sky where there are these gaps, you could see the sun shining through.  So, what we want is to find these holes or the gaps in the cloud cover.  And this is one of the examples how the galaxy is able to create the gaps through which the light can sort of just really stream out.

Kat -  What do your results tell us about the formation of the early universe?

Sanchayeeta -  The earliest galaxy we have discovered so far, it is a very compact star forming galaxy.  It has similar properties.  The size of the galaxy is very similar.  It is forming similar amount of stars and it has similar amount of stars already.  So, it's look like, if you look at this galaxy that we have in the nearby universe, this is what it would look like.  And that's why we think that we can translate what's going on in this galaxy.  And that is that it's so massive and so compact that together, it can really create havoc on the parent cloud and create these gaps, and let the ionising photons escape.

Kat -  Sanchayeeta Borthakur.

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