It seems that finding our Milky Way’s twin has become a bit of an industry these days.
NASA/ESA have got in on the act today, releasing a press release about their favourite twin of the Milky Way, NGC 1073 and the below absolutely gorgeous Hubble Space Telescope image they’ve taken of it: Classic Portrait of a Barred Spiral.
And it does look a lot like what we think the Milky Way looks like – except perhaps for having slightly less tightly wound arms.
You might remember, back in September I posted a guest blog by Portsmouth A-level student, Tim Buckman, who spent his summer with us at Portsmouth finding the Galaxy Zoo galaxy we thought was most like the Milky Way: “A Summer Spent Finding our Galactic Twin “. His project in turn was inspired in part by an ESO press release about spiral galaxy NGC 6744 which was claimed to be a twin for the Milky Way (A Postcard from Extragalactic Space).
NGC 6744 is quite a lot more massive than our Milky Way however, so I thought we could do better with SDSS and Galaxy Zoo. Tim applied some mass cuts, then used your classifications to find a face-on 4 armed spiral which he thought matched the maps of the Milky Way (which has a bar, but perhaps a rather weak one which might not be obvious in the types of images we used for Galaxy Zoo).
I was interested to notice last month that one of the most popular press releases from the AAS this year was about finding a sample of galaxies like our Milky Way and using them to estimate what the colour of the Milky Way would be (BBC Article: Milky Way’s True Colours; AAS abstract it’s based on: What is the Color of the Milky Way?), especially interesting to me as it turns out the Milky Way might be on it’s way to being a red spiral (as has been suggested before, e.g. by Mutch, Croton, Poole (2011), or see New Scientist article about this paper: Milky Way Faces Midlife Crisis), which you might remember I’ve done a bit of work on! 😉
Today’s NASA/ESA release has already been picked up by the BBC: Hubble Snaps Stunning Barred Spiral Galaxy Image (they’d already used “Striking View of Milky Way Twin” on NGC 6744), and Space.com covers it as Hubble Telescope Spies Milky Way Galaxy Twin.
For Galaxy Zoo people, it should be of interest that the press release also says:
Some astronomers have suggested that the formation of a central bar-like structure might signal a spiral galaxy’s passage from intense star-formation into adulthood, as the bars turn up more often in galaxies full of older, red stars than younger, blue stars.
Well those astronomers are us – Galaxy Zoo results on bars, based on your classifications have shown that bars are more common in redder discs. Thanks again for the classifications which allowed us to do that work.
Today’s post is a guest post by A-level Student, Tim Buckman from Portsmouth Grammer School, who spent 6 weeks working with me at Portsmouth University this summer through the Nuffield Science Bursery Scheme.
Finding Our Galactic Twin
For millions of years humans have attempted to understand their place in the cosmos.
We went from the flat Earth to the globe; from a geocentric to a heliocentric solar system, and now we understand we live in the outskirts of a spiral galaxy – a massive collection of stars.
For years though astronomers have endeavoured to find out what The Milky Way, our home galaxy, actually looks like in detail. The difficulty lies in the fact that we live within it, and it would take thousands of years of travel to get a good photo opportunity. The best models suggest that our galaxy is a spiral galaxy with between two and four spiral arms, a central bulge and a bar at the centre. Using what data we have, artists have tried to create an impression of our galaxy’s structure and form, the best guess being the one below.
Recently, the European Southern Observatory released an image of a galaxy which they called as a twin for our own. On the face of it the galaxy (below) looks just like our own, it has a similar number of spiral arms, it has a central bulge and, if you look closely, even a small bar at the centre. It’s name is NGC 6744 and from July of this year, it became our Galaxy’s twin. There is a small problem with this galaxy however, or should I say, a large problem; this galaxy is actually twice the size of our own in mass and size and therefore is a bit of a stretch to suggest it as a copy. We are again stumbling in the dark to find more about where we live.
This is where the Galaxy Zoo project CAN help. It aims with the help of ALMOST 450,000 volunteers, to classify as many galaxies as possible from the Sloan Digital Sky Survey. By using this information, we can start to narrow down a list of galaxies to look at. By filtering out those which were seen to have features and were relatively face-on to the camera, we end up with a list of around 17,500 galaxies in total. Again by filtering out those galaxies with the same mass, number of spiral arms and having a bar like the Milky Way, we find that there are just 9 galaxies which fit this criteria. Of these nine galaxies, the one which looked the most like the artists impression was the one shown below. This galaxy, captured through the Sloan Digital Sky Survey (SDSS) camera is the most likely of the galaxies we have seen to be a clone of our own.
The fact remains that this might, possibly, not be the best Milky Way ‘clone’ in the universe, there are countless galaxies yet to be photographed and there are thousands of galaxies which, due to their orientation, make it very difficult to see whether they are anything like ours. However, with rapid advances in technology, this dream of finding the shape of our galaxy is just around the corner.