Hello Space Fans and welcome to another edition of Space Fan News.
This week, astronomers probe deeper than ever into the famous patch of sky known as the
Hubble Ultra Deep Field with the Atacama Large Millimeter/submillimeter Array; and an international
team of scientists learn more about how very high-mass stars are made.
For ten years now I have been telling you about this tiny, rather unremarkable patch
of sky where, if you looked up at it with your naked eye, is rather unremarkable.
This region of sky is about seven hundred times smaller than the area of the disc of
the full Moon as seen from Earth.
It had no obvious stars, gas clouds or anything else in it.
Astronomers chose that patch of sky for Hubble to stare at for days for that very reason.
They wanted to see what pointing the most powerful telescope ever built at absolutely
nothing would show.
The results are now legendary: over 10,000 galaxies were found in that tiny patch of
sky and we were forever changed by what that represented.
Well last month, astronomers pointed the most powerful radio telescope in the world at the
Hubble Ultra Deep Field to see what they could find.
ALMA, or the Atacama Large Millimeter/Submillimeter Array, explored this distant corner of the
universe for the first time in millimeter wavelengths.
These wavelengths allows them to see the faint glow from gas clouds as well as the emission
from warm dust in galaxies in the early Universe.
ALMA has observed the HUDF for a total of around 50 hours.
This is the largest amount of ALMA observing time spent on one area of the sky so far.
Most of the galaxies in the Hubble Ultra Deep Field existed during a time in the early universe
where starbirth was at its peak, come 10 billion years ago.
While they may not look like much, these galaxies are producing stars like crazy, and ALMA gave
us a glimpse into why that may be happening.
There were two different teams looking at two different things.
The first team looked at the emission from warm gas in the early universe and found that
the warm gas matched up very nicely with the galaxies seen by Hubble.
So far, so good.
They were able to connect the visible and ultraviolet observations by Hubble with the
millimeter observations with ALMA.
The ALMA Observations also showed a connection between the number of stars in a galaxy and
it’s star formation rate.
High mass galaxies, those with stellar masses greater than 20 billion times that of the
Sun, all showed up really bright in ALMA data.
For comparison, the Milky Way is a large galaxy and has a mass of around 100 billion solar
masses.
This meant that high mass galaxies also showed high star formation rates.
The second team used ALMA to image the cool gas, which in particular gave them a glimpse
into the amount of Carbon Monoxide in the gas, something Hubble can’t see.
Carbon Monoxide is an indicator that a galaxy is really primed for star formation.
These observations confirmed that the farther we go back in time to the early galaxies,
the more gas content a galaxy has, which in turn means it can make more stars.
Astronomers have known for a while now that star formation peaked in our universe around
10 billion years ago, and thanks to Hubble and now these new observations from ALMA,
we have a better idea as to why: there is plenty of warm and colder molecular gas in
the early galaxies, and the earlier we go, the more of it there seems to be.
These results are just the start of a series of future observations to probe the distant
Universe with ALMA.
For example, a planned 150-hour observing campaign of the HUDF will further illuminate
the star-forming potential history of the Universe.
I’ll keep you posted.
Next, speaking of the early universe, many of those stars formed some 10 billion years
ago were very strange stars: hundreds of times more massive and only lived a few hundred
million years.
Understanding how massive stars form has always been a top priority for astronomers and this
week, we’ve gotten a little bit closer.
Astronomers using the Gemini North Observatory on Maunakea in Hawai‘i have found the strongest
evidence yet that the formation of more massive stars follow a path similar to lower-mass
stars but way bigger!
As stars form, slowly coalescing from clouds of gas and ultimately forming an accretion
disk of material that will one day form a star, along the way, astronomers have noticed
- that for average stars like our sun at least - these episodic bursts of energy that come
out of the clumps in the accretion disk as the star forms.
Well it turns out that these outbursts happen when very massive stars form too, only they
are way bigger.
These outbursts, which are several orders of magnitude larger than their lower mass
siblings, can release about as much energy as our Sun delivers in over 100,000 years,
What this means is that massive stars don’t just show outbursts when they die - for example
supernovae - but they also have outbursts when they form.
Don’t you just love to see symmetry in nature?
While it may seem obvious that smaller stars that have outbursts as they form should also
be evident when larger stars form, it really isn’t.
It wasn’t clear that massive stars could even form from clumpy accretion disks because
the energy involved in making these stars should destroy the disk.
Yet somehow they survive and astronomers aren’t sure why, but these observations show that
massive stars most definitely can form from a clumpy accretion disk condensed from a cloud
of gas.
Studying the formation of high-mass stars is hard because they are relatively rare and
deeply embedded in their natal cloud, which makes them not visible in visible, light.
These observations are an example of why we need infrared detectors.
These outburst events are also very rapid, probably lasting only a few years or less
- which, for a star, is the blink of an eye, adding to their rarity.
The developing star observed in this study, S255IR NIRS 3, is relatively distant, some
6,000 light years away, with a mass estimated at about 20 times the mass of our Sun.
The Gemini observations reveal that the source of the explosive outburst is a huge clump
of gas, probably about twice the mass of Jupiter, accelerated to supersonic speeds and ingested
by the forming star.
The team estimates that the outburst began about 16 months ago and it appears that the
outburst is still active, but much weaker.
Understanding how high mass stars form has always been hard, but now with observatories
like Gemini, we are inexorably marching forward.
Well, that’s it for this week Space Fans thanks to the Planets Foundation for sponsoring
SFN this Month, thanks also to all of the SFN Patreon Patrons who make sure Space Fan
news gets produced each week, thanks to all of you for watching and as always, Keep Looking
Up!