Milky Way Astrophysics from Wide Field Surveys - Part II

The second day of the Wide Field Surveys meeting has covered a wide range of topics, from the formation of stars, the lives of massive stars, to more evolved stars and even dying stars such as supernovae.

One of the most interesting results presented today came from a sub-mm survey of the Serpens star forming region using the James Clerk Maxwell Telescope in Hawaii. Using this data a group of astronomers have been searching the images for outflows coming from young stars, which is thought to be a common occurrence during the star formation process as a by-product of how stars accrete material from their surroundings.

Outflow coming from the Herbig-Haro object HH47
(Credit: HST/NASA)

After studying these outflows the astronomers were able to calculate the amount of energy that the outflows were injecting into the surrounding molecular cloud. They found that the energy injected from the outflows was as high as 70% of the total turbulent energy within the cloud. Turbulence is the name given to the energetic motions within molecular clouds, and which is thought to be responsible for preventing the molecular cloud from collapsing under its own gravity.

This result suggests that one of the most important mechanisms for preventing molecular clouds from collapsing is the outflows produced by the stars that form within them! Because molecular clouds need to collapse to form stars, outflows are actually limiting the amount of further star formation that these molecular clouds can produce. Astronomers call this feedback, the influence of stars that have already formed on the surrounding molecular cloud, and it's exciting to see it happening in this region.

Milky Way Astrophysics from Wide Field Surveys - Part I

The entrance to the Royal Astronomical Society's
headquarters at Burlington House in London
(Credit: Wikimedia Commons)

This week I'm at a conference in London at the headquarters of the Royal Astronomical Society where we're discussing scientific results from recent wide field surveys of the Milky Way. Wide field surveys is just another name for surveys that cover a large area of space, and there are many surveys these days that fit that category, including a few that I work on.

Because these surveys cover such a large area of space they allow many different types of astronomical objects to be studied, from young stars to old stars, individual objects to the entire galaxy. So a conference like this is a great opportunity to stay in touch with a wide array of scientific results.

Today's talks have mostly been given by the leaders of the surveys, who have been telling us about their surveys, how we can get the data from the surveys, and highlighting some of the scientific results. This is a good opportunity to learn about new survey data and to think about how this data might be useful to solve some of the problems I'm trying to address.

The Milky Way - home of many many surveys! (Credit: ESO)

I've been really impressed with the surveys presented today. They've covered (almost) every part of the electromagnetic spectrum, from radio waves through the infrared and up to the optical part of the spectrum, and they've offered up a huge range of possibilities for future work. They also have some amazing names, including such gems as e-MERLIN and UWISH - astronomers really love acronyms!

The highlight of the day for me was probably a presentation about a sub-mm survey called ATLASGAL. The sub-mm part of the electromagnetic spectrum is between the infrared and the microwave parts of the spectrum. One of the advantages of observing in this part of the electromagnetic spectrum is that it is not absorbed by dust and so can be used to study objects across our entire galaxy, even on the far side of our galaxy that would normally be obscured and inaccessible to us.

Part of the Galactic Plane of our galaxy seen by the ATLASGAL survey showing a number of prominent
star forming regions, including Messier 20, The Triffid Nebula (Credit: ESO/ATLASGAL)

The survey data has been used by a team of astronomers to survey the majority of our galaxy in the sub-mm part of the spectrum and identify hundreds of dense clumps of molecular gas where massive stars are forming. Sub-mm emission is one of the most reliable and efficient methods to identify dense star forming regions. It's an exciting project and I'm looking forward to seeing more results from the survey in the future.

The massive stars of Cygnus OB2

A couple of weeks ago I talked about an OB association known as Cygnus OB2, one of the largest groups of young stars in our galaxy, and an exciting location to study star formation on the grandest scales. This week I want to tell you about some research I recently carried out to better understand this region, research which has recently been published.

The Cygnus OB2 association, as seen though a combination of
X-ray (blue), optical (yellow) and infrared (red) light
(Credit: Chandra X-ray Observatory)

There has been a lot of work carried out recently by many other astronomers to understand some of the really massive stars in Cygnus OB2, which are all very interesting objects, many of which are unique and can tell us exciting things about how massive stars live their short and turbulent lives. Thanks to this work we're now in a position to put all this information together and use it to better understand the entire group of stars as a whole, and that's what I did!

I was able to gather information about 169 massive stars in Cygnus OB2, including some stars as massive as 100 times the mass of our Sun. For each of these stars I was able to determine their mass and age, by comparing their measured properties with the predictions from models of how massive stars evolve throughout their lives. One of the main advances in astronomy over the last few decades has been the development of models that describe not just how stars change throughout their lives, but how they appear during this time. These models, known as stellar evolution models, allow astronomers to estimate how old and how massive the stars that they see are.

The positions of massive stars (red, green and yellow dots) across the Cygnus region, shown against a black and white infrared image of the region. The white circle denotes the area covered by Cygnus OB2 and studied in my paper
(Credit: Nick Wright)

With this information we were able to determine the approximate ages of all the massive stars, allowing us to determine what's known as the star formation history of the region. The star formation history tells us when all the stars formed, and that's important to know if we want to understand how massive OB associations like this formed.

The simple view would be that all the stars formed at the same, or at least very similar, times. This is what's known as instantaneous star formation, or star-burst, because all the star formation occurs in a quick burst when the conditions in the molecular cloud become right for star formation.

The centre of the Cygnus OB2 association - or is it multiple associations?
(Credit: Nick Wright)

However that wasn't what we found. Instead we found that the ages of the stars were spread out over quite a long time period, almost 10 million years. That's a long period of time for star formation, because most astronomers think star formation occurs quickly, within only 1-2 million years or less. But here we're seeing that the star formation didn't happen all at once but was spread out, happening almost constantly for 10 million years.

What does this mean? Is the star formation that has occurred here any different from star formation taking place elsewhere? Probably not. What probably happened here is that the star formation didn't just take place over a long period of time, but probably also took place over a large area of space, almost like multiple small star formation events! These individual star formation events have since merged and combined so that we see them now as this large and homogeneous group of young stars.

It's a theory anyway. One of the great joys of science is discovering something you didn't expect to find, thinking of a new theory to describe what you saw, and then testing your theory. Science is not set in stone but is continually evolving with new theories being proposed, and existing theories being tested, and then refined or discarded. We call this the scientific method, and it underpins all of science.

You can read the full paper here if you're interested to learn more.

Total Solar Eclipse on March 20th

This week sees the first Solar eclipse of 2015, and the only total Solar eclipse this year. The eclipse will be partly visible to observers across Europe, northern Africa, and western Russia. However the only places where the Solar Eclipse will be visible in totality will be the Faroe Islands, large parts of the North Sea, and Norway's Svalbard Islands. There's a map showing where the eclipse will be visible from here.

A photography showing roughly what the Solar Eclipse on Friday will look
like from the UK (Credit: Mr Eclipse)

Observers in the UK, Ireland, Scandinavia, and Iceland can expect to see at least 80% of the Sun's disc being occulted, providing the clouds don't get in the way. The eclipse will begin at around 8.30am GMT and will reach maximum occultation, regardless of your location, at about 9.40am GMT, before taking another hour for the Moon to pass away from the Sun.

This is a great opportunity to see a solar eclipse and for those in the UK who missed the 1999 eclipse due to clouds it might be the best opportunity to see an eclipse from home. I would recommend everyone to step outside of your workplace sometime between 9 and 10am (preferably as close to 9.40am as possible), and have a look.

It goes without saying that you should never look directly at the Sun, even during a total eclipse, but there are other easy ways to view a total eclipse in complete safety. One easy method is to acquire a pair of eclipse shades, which are really just extreme sunglasses that dim the light from the Sun and will allow you to see the eclipse (they're even safe to use to look at the Sun during normal daylight hours). These can usually be acquired from museums or observatories, so check your local listings if you want to get a pair.

If you can't find any eclipse shades then another alternative is to make a pinhole camera to view the eclipse. This is actually surprisingly easy and cheap to do! All you need is a large sheet of cardboard into which you cut a small hole, roughly the size of a coin. Then put a piece of thick black tape over that hole so that it covers it entirely. Then use a pin to poke a very small hole in the tape. Then during the eclipse you can hold up the piece of card and let the light from the Sun pass through the pinhole. If you position the card so that the light passing through the pinhole falls onto a flat, light-coloured surface then you'll be able to see an image of the Sun on that surface. This is effectively how the aperture of a camera works. You can even test your pinhole camera in advance to project an image of the un-eclipsed Sun!

I hope you all enjoy the eclipse this Friday, have fun!

NASA's Dawn mission arrives at Ceres

Exciting news this weekend from NASA's Dawn mission, which went into orbit around the dwarf planet Ceres after a successful orbital manoeuvre. It became the first ever man-made satellite to orbit a dwarf planet, and only the seventh planet of any sort to achieve such status.

Two views of the dwarf planet Ceres, as seen by NASA's Dawn mission as it went into orbit around
the dwarf planet on Friday (Credit: NASA)

Ceres, named after the Roman god of farming, was discovered on New Year's Day 1801 by Giuseppi Piazzi, and at the time was the 6th celestial planet to be discovered. A few years later another planetary body was discovered in the same region and named Pallas.

These two objects were noted by astronomers to be significantly smaller than the other planets and could not be resolved into a disc like the other planets, even with the best telescopes of the day (Ceres itself is less than 1000 km wide, a fraction of the size of our Moon). Because of this, Sir William Herschel proposed in 1802 that these two objects be re-labelled as asteroids, from the Greek meaning star-like.

Many more asteroids were discovered in the same region of space throughout the 19th century leading to the idea that these asteroids were distributed in a ring between the orbits of Mars and Jupiter, a ring which came to be known as the asteroid belt. Ceres, which is sometimes referred to as a dwarf planet, is the largest object in the asteroid belt, composing approximately a third of the total mass of all the objects in the asteroid belt. Ceres could therefore be very important for understanding the origin of the asteroid belt and for learning more about how our Solar System formed.

Now the Dawn Mission is in orbit around Ceres we can expect some beautiful images and many interesting scientific discoveries in the near future, hopefully starting with some explanation of what that bright white spot on the surface of Ceres is.