stars

Hubble reveals a sparkling spectacle in the LMC

A section of the new Hubble image showing the star cluster R136 and surroundings.
Credit: NASA, ESA, and F. Paresce (INAF-IASF, Bologna, Italy), R. O’Connell (University of Virginia, Charlottesville), and the Wide Field Camera 3 Science Oversight Committee. Click for a larger version.

I’ve thought hard about how I might write this post. How do you go about introducing the incredible image above?

I could tell you that it’s a new image taken by the Hubble Space Telescope’s shiny new Wide Field Camera 3. I’d probably say that it shows a region of frenetic star formation in the Large Magellanic Cloud (a nearby galaxy to the Milky Way) known as 30 Doradus. Undoubtedly I’d draw your attention to the cluster of stars to the centre right of the image, designated R136. It’s full of infant massive stars whose winds are sculpting the gas around the cluster; seen clearly in the great, roughly 70 lightyear wide, cavern forming at the centre of the image. I’d likely also talk about the huge billowing clouds of hydrogen gas which are glowing red around the young cluster – a typical trait of star forming regions. And I’d definitely say that using Hubble to study regions like this one allows astronomers to examine the processes which create and shape the stars in vast stellar clusters like R136.

Of course, in the end, the image speaks for itself in many ways; its sheer beauty, the vivid colours, the stunning detail that shows the power of the instrument that made it. We’re going to miss Hubble when it’s gone. But images like this one show that it’s got a lot more to offer before that time comes.

Milky Way’s black hole confirmed and more!

esogcimage2The stars at the centre of the Milky Way, in infrared. Credit: ESO/S. Gillessen et al.

My colleagues at ESO have just published a press release I worked on about a study into the black hole at the centre of our galaxy — the Milky Way. The release is the largest one I’ve done to date, and great fun to do too — not least because of the several fascinating intertwined stories within it. I’ll start with the big one though.

That is, a 16 year long study by astronomers (from the Max-Planck-Institute for Extraterrestrial Physics in Germany) has given us the best empirical evidence, so far, of the existence of truly massive black holes. Not only does the evidence verify the existence of these leviathan objects, it also shows that one is “beyond any reasonable doubt” hiding at the heart of the Milky Way, with a mass of some four million times that of the Sun. Here’s a section from the start of  the release:

“By watching the motions of 28 stars orbiting the Milky Way’s most central region with admirable patience and amazing precision, astronomers have been able to study the super-massive black hole lurking there. The new research marks the first time that the orbits of so many of these central stars have been calculated precisely and reveals information about the enigmatic formation of these stars — and about the black hole to which they are bound.”

esostarsintheirorbitsAn artist’s impression of the orbits of the central stars. Credit: ESO

Incredibly, over the course of the study, one star (known as ‘S2’) was even able to make a complete orbit of the Milky Way’s hub. Yet it gets even better. Thanks to the observations we can now watch S2 whirl around (with all its companions) in actual infrared images from ESO’s telescopes, taken over the 16 years. The telescopes use adaptive optics to counteract the problems associated with trying to observe through Earth’s turbulent atmosphere. Observing in the infrared also allows the telescopes to penetrate the thick dust and gas of the Galaxy, and thus peer straight at these intriguing central stars. You can watch the animation of these real images in a (7MB) Quicktime video here. The motion of the stars has been sped up by just over 30 million times!

s2A frame from the video (see link above). Credit: ESO/ R.Genzel and S. Gillessen

If you want to get the full story you can read the whole press release here. There are some great videos to go with the article so be sure to have a look at them on the ESO webpage. And of course check out the second episode of the ESOcast (summarising the result), here. It’s great to see that, already, this fascinating result has sparked the interest of some major news outlets including here, here and here.

The stellar wolves in sheep’s clothing

Looking at this stunning new picture* from the European Observatory (below) you’d be forgiven for thinking that this is a region of calm beauty, hanging in interstellar space. This is the object known as Gum 29 – a huge nebulous region of ionised hydrogen gas sitting around 26,000 light-years from Earth just on the outer part of the Carina spiral arm of our galaxy, the Milky Way. Whilst the swirling clouds of gas do look serene, they are detracting from a maelstrom of violence which is being perpetrated by two massive stars within the cluster, at the heart of the nebula. The cluster is known as Westerlund 2 and it is the location of a binary star system (known as WR20a) composed of two huge stars with masses of 82 and 83 solar masses.

Gum 29 hides a secret. Credit: ESO

These stars are on the verge of dying and are classified by astronomers as ‘Wolf-Rayet’ stars. These are stars that are ejecting huge quantities of material (like gas and dust) as they go about the last stages of their lives. As they eject this material it is lofted on strong stellar winds which rush away from the stars at incredible rates, sometimes as quickly as several thousand kilometres every second. The binary star system of WR20a is circling every 3.7 days and as it does the stars’ respective winds buffet each other.

The result is a violent collision of gas which prodcues a flood of X-rays, that can be seen by X-ray observatories like the Chandra Observatory orbiting Earth. This blast of X-rays can be seen in the X-ray image here (from Chandra) as a yellow fuzzy blob, towards the bottom right of the cluster. You can also see the (visible) light, from the system, in the image below. In time the stars of the WR20a system will  die, as their cores collapse, most likely creating a blast known as a supernova. That’s going to be an incredible sight when it happens and we’ll have a front row seat, if we’re still around.

The binary system WR20a. Credit: ESO

Astronomers are interested in studying these incredible objects as they can then get a better understanding of what happens to massive stars at the end of their lives and refine their models of stellar evolution. It’s thought that most extremely massive stars in the Universe will behave like WR20a and become Wolf-Rayet stars prior to exploding as supernovae. But there are still some stars which throw the proverbial spanner in the works. Take Eta Carinae for example (below). It’s an odd, extremely massive, rare type of star known as a luminous blue variable. It’s been expelling huge amounts of material for a long time and is four million times more luminous than our own, rather meagre in comparison, Sun.  Today we see the star surrounded by two huge lobes of pinkish gas, each formed during one of the star’s larger ejections, seen to appear in the early 1840s. Some astronomers think that Eta Carinae is exhibiting Wolf-Rayet star like properties due to this extreme behaviour, and may even be on its way to becoming one. But astronomers from the Gemini Observatory have recently found that the material moving out from Eta Carinae is travelling much faster than if it was being swept on fierce stellar winds.

Eta Carinae. Credit: Jon Morse and NASA/ESA

They have found that the gas and dust flying away from the star is moving away (at speeds up to 6,000 km/s) with a little less energy than you might expect from the blast of a supernova. Below you can see a wonderful animation depicting the scenario, with a blast wave emerging from the star. That blast wave excites the gas from previous ejections and we begin to see the familiar shape of the two lobes around Eta Carinae, that we see today. But the star hasn’t gone supernova, so what’s going on? Well astronomers don’t quite know at the moment and so it seems Eta Carinae has become just that little bit more interesting and peculiar. Some argue that perhaps Eta Carinae is similar to other stars which appear to have released an explosive amount of energy at the end of their lives, yet haven’t gone supernova. However, as yet, there’s no concrete theory on how these  stars might evolve (at the end of their lives) and what may trigger their violent ejections. Maybe we are looking at a new type of stellar explosion? Even so, if we aren’t sure what’s happening with Eta Carinae, will we actually have enough time to study it to find out? Well the answer is yes, it looks as if we’ll have a little while yet. Astronomers from ESO think that it might be 10,000 years from kicking the bucket. That’s still very soon in the lifetime of a star mind you. Nevertheless, it appears that Eta Carinae is going to be intriguing, at least several, generations of astronomers for millenia to come.

Eta Carinae’s expanding shells. Credit: Gemini Observatory, artwork by Lynette Cook.

*I recently finished writing the press release for the Gum 29 image and you if you’re interested you can read it in full on the ESO website here.


Super sharp Hubble shows stars in nearby galaxies

The Hubble Space Telescope is renowned for its incredible resolution used in studying the depths of the Universe – from the earliest galaxies to some of the grandest spirals. Recently though it has been using these superb capabilities to observe nearby galaxies – that is, a selection of galaxies between about 7 and 13 million light years from the Earth.

Above: Hubble’s resolution has revealed NGC 253 as a swirl of countless stars and dust lanes, enabling new insights into the character and structure of this beautiful galaxy.

At this time of year I love to get out a wide-field refracting telescope and use it to spot the relatively bright galaxies M31 (the Andromeda Galaxy) and M33. Through the eyepiece they appear as bright smudges of light, M31 being slightly elongated in shape. Those smudges are in fact the accumulated light of billions of stars shining away brightly, inside their respective galaxies. Yet we can’t see the individual stars in the galaxy with our amateur telescopes because their resolving power is simply too low, they appear blurred and merged together. But with Hubble things are much different.

When it looked at 69 nearby galaxies, its powerful optics were able to show individual stars and glittering star clusters within them. This ability to look at the fine detail has allowed astronomers to make important studies into the lives of these stars, how they are born and more. Astronomers can then also use the observations to make detailed conclusions about the shape and structure of the (often intricate) galaxy they are studying.

We can liken some of the previous observations to trying to understand how the population of a city lives, interacts and moves around, just by looking at a street-map. With Hubble’s brilliant resolution astronomers have been able to get a far more detailed view of the lives of galaxies and their stars – we can study the people in the street as it were. As Benjamin Williams, of the University of Washington says in the ESA press release “With these images, we can see what makes each galaxy unique”.

Left: A maelstrom of thousands upon thousands of individual stars reveals itself in this Hubble Advanced Camera for Surveys image of NGC 300, some 7 million light years away from Earth.

These observations are important because it is essential for astronomers to build an understanding of galaxies close to the Milky Way, in order to investigate (and hopefully understand) those which might be subtly different in the farther, or even extremely distant Universe. How are stars forming and how fast? Where are the old stars and why are some galaxies so massive? These are all questions which studies like these look to answer. Thankfully the survey which Hubble was working on (the ANGST or ACS Nearby Galaxy Survey Treasury) is wide ranging and shows a diverse sample of galaxies. It aims to create a practically complete study of all the galaxies in what is known as the Local Neighbourhood. So slowly but surely we are getting to know our cosmic neighbours!

Meanwhile, with the Hubble Servicing Mission 4 postponed until further notice (due to an anomaly with Hubble’s control unit) we are going to have to sit back and wait patiently to see if, and when, Hubble can get back to doing its usual spectacular science.

Image credits – Top; NASA, ESA, J. Dalcanton and B. Williams (University of Washington), T.A. Rector/University of Alaska Anchorage, T. Abbott and NOAO/AURA/NSF: Left hand side; NASA, ESA, J. Dalcanton and B. Williams (University of Washington)