The 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.”
An 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!
A 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 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)