Unveiling the Mass of Galaxies with Vera Rubin

This week I am attending a conference at Queen’s University in Kingston (Ontario, Canada) with I think the longest name I have ever seen. It’s called “A Celebration of Vera Rubin’s Life. Unveiling the Mass: Extracting an Interpreting Galaxy Masses.” I was very excited to attend this conference. Vera Rubin has always been a role model of mine (hard to avoid as a women studying galaxies) and as well as her the list of speakers includes many people who’s work I know and respect. It also has the advantage of being held in Kingston where a close friend (and fellow astronomer) from graduate school is now living with her very new baby.

This morning the introductory talks did not disappoint. We heard anecdotes from Vera Rubin about her work as a young scientist just trying to interpret the observations she was making on the rotation curves of galaxies (observations that provided the first strong evidence for dark matter in galaxies). She talked about a 1962 paper she did with students measuring the rotation curve of the Milky Way, and her regrets on not noticing that dark matter must have been present when she measured a similar “flat” rotation curve for the Andromeda galaxy 13 years later. She further impressed me by dating another anecdote (about discovering a galaxy in which the stars rotated in two directions) by the year her youngest child learned to walk (1961). Not only is Vera Rubin an incredibly successful and famous astronomer, but she managed to have 4 children (at least one of whom followed her into astronomy) during the period she did most of her famous work. Wow! I got to talk with her a little bit this morning at coffee, and she’s also a very nice person.

As well as enjoying the many talks by leaders in the field of galaxy evolution, I am presenting a poster on my work on dust reddening of Galaxy Zoo spirals which you have heard about several times before (eg. Blue Sky and Red Spirals, and from when I presented it at the 2009 European Week of Astronomy). This work has relevance to the masses of galaxies as dust is a significant source of error on estimates of the total mass of stars in a galaxy – at the simplest level dust hides the stars.


I was encouraged to share my poster on this blog, so if you wish to have a closer look at it you can download it (pdf). Of course this poster is aimed at explaining my work to other astronomers not to a general audience. If you have questions about it I encourage you to first look at my more general explanation of the work Blue Sky and Red Spirals and I am also happy to answer questions in the comments below.

One little details which is not explained in the poster is that the images of galaxies on both the right and left are not random. On the right I show edge-on spiral galaxies ordered from bluest (at the bottom) to reddest (at the top). On the left I show all face-on galaxies, also ordered in the same way. My definition of blue versus red comes from a measured difference in the brightness seen through 2 filters (in this case the SDSS g and z filters), so is not always obvious to the eye – also remember that it is the average colour of the whole galaxy, and some have significantly different colours in their centres to in the outskirts. However one of the interesting results coming from this work is that even though on average dust reddens galaxies as they become more inclined (as they go from face-on to edge-on) some face-on galaxies are much redder than some edge-on galaxies. This shows that while dust is important to the colour of a spiral galaxy it is clearly not the most important factor. This is very good news for those of us interested in red spirals as an evolutionary stage!

If anyone is in the Kingston area there will be a public lecture at 8pm tomorrow night given by Prof. Sandy Faber. It’s on the Queen’s Campus in the Biosciences Building, Room 1101. I include the poster below. Sandy Faber was a student of Vera Rubin’s and gave a very nice review talk this morning about her early work on dark matter during this time. I encourage you to attend if you are able – I think it will be a very nice public astronomy talk.


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About karenlmasters

Professor of Astronomy and Physics at Haverford College, USA. Project Scientist for Galaxy Zoo. Spokesperson for the Sloan Digital Sky Survey. Busy having fun with astronomy!

10 responses to “Unveiling the Mass of Galaxies with Vera Rubin”

  1. Kevin says :

    If you look at the bottom of Karen’s poster, you might just spot your name…. ; )

  2. Thomas says :

    Great work and a great blog post, Karen. The angle of inclination versus reddening is particularly interesting. Great, too, that you got to meet one of your role models.

    Thanks for the blog and good luck in your future work.

  3. Alice says :

    Ooooh, thank you very much indeed for this, Karen. I’ve been wondering ever since I started beta-testing zoo II whether the galaxies with large bulges weren’t the older ones, and your statement “Bulgy spirals have
    less dust than disky spirals” sounds (to an amateur) like it – more elliptically. Or have I got that completely wrong? What happens to a spiral galaxy that simply gets so old it runs out of gas and dust to produce star formation? Would it become red not due to strangulation but simply due to age? I have seen very few flat red spirals . . . . on the other hand I may simply be getting carried away with my own shaky interpretations. Please let me know.

    And it was nice to hear about some other astronomers too. For all my zoo work I’d never even heard of Vera Rubin. Have to look her up. Enjoy the conference!

  4. Karen says :

    Thanks for the nice comments. It has been great to meet a role model – and in fact I ended up sitting on her table for both lunch and our dinner boat cruise, so I got to hear a lot more anecdotes and learned a lot. I also had a very interesting conversation with her astronomer daughter (Judith Young). My daughter is only 2, so I have a while to worry about the impact my career will have on her life choices, but it was great to get some advice from someone who’s both a daughter of an astronomer, and an astromer who’s a mother of a daughter. Can’t be too many of them around yet!

    Alice – you’re absolutely right that spiral galaxies with large bulges are in some ways older than spiral galaxies with small bulges. Both types of spirals may have very recent star formation (blue stars) in their disks, but almost universally we see that the bulges of galaxies have much older ages and redder colours than the disk. So if you have a galaxy with a larger bulge – then its average age is dominated more by the old stars in the bulge and so is older.

    What’s interesting about the red spirals though is that we see spirals with red disks. In fact Galaxy Zoo 2 will really help to pick these out better. Not only will we be able to find the red spirals and blue ellipticals, but Zoo 2 will help us find the blue spiral bulges and red spiral disks. They will both be very interesting classes of objects and give a lot of insight into galaxy evolution.

  5. zeus2007 says :

    First of all please allow me to congratulate all those wonderful ladies studying the cosmos and trying to understand the whole purpose of human existence. I am truly, and humbly, glad and very happy to hear that women are now our powerful mentors in understanding ourselves. The info posted here is simply fantastic, how good it must feel to unlock a little piece of a mystery which has marveled scientist for a long time. It is indeed a very fascinanting subject, and, if I may, I’d like to wish all of you madames the best in any future endevour, or journey, you ladies embark on.

    With sincerest respects,

  6. Alice says :

    Just been to Wiki to check out Vera Rubin. Wow, she found out some cool stuff, and studied under some fantastic scientists! As well as being one herself, that is – I’m looking at her university career . . . which is worth checking out. She wanted to study graduate astronomy at Princeton University and they didn’t even send her their catalogue because the course didn’t accept women until 1975!!!


    Now to go and read up on the galaxy rotation stuff 😀

  7. Karen Masters says :

    Isn’t the Princeton story awful. I just got back from the conference banquet where we heard that (and many other, both positive and negative) anecdotes from Vera herself. Sandy Faber got up after Vera Rubin to say that Princeton did the same to her 20 years later! I didn’t know it was 1975 before they accepted women…

    However on a positive note Vera and Sandy also both told stories about their children – who apparently grew up thinking only women could become astronomers! There’s some very clear insight into how humans think to be had by putting those two stories together!

    If Vera was a role model/hero of mine before this conference then…. well it’s certainly increased my respect for the example she has put forward as a scientist, mother and all around great person.

  8. Joseph H Murray says :


    This is a somewhat thought out relation of ‘Dark Matter’ to to Hugh Everett’s ‘Many-Worlds’.

    You could consult with VERA RUBIN to get a professional opinion of the idea.

    It has occurred to me that the unknown source of ‘Dark Matter’ may be the material of new universes
    escaping to other worlds in Everett’s ‘Many-Worlds’ theory.

    The strongest clue is that both ‘Dark Matter’ and the ‘Many-Worlds’ involve huge, huge amounts
    of matter.

    A second clue is that the escaping ‘Many-Worlds’ material might be invisible in present day
    telescopes. This is a requirement for ‘Dark Matter’.

    A third clue is that I would expect that the escape time of ‘Many-Worlds’ material to be very short.

    For a description of ‘Dark Matter’ please look up both FRITZ ZWICKI and VERA RUBIN.

    If you get a positive response from VERA RUBIN, it would be great publicity for your
    book on the life of HUGH EVERETT!!!

    Have a great day!!!!

    Joe Murray

    hazjoe@gmail.com (My MAC)


    jhmurray@me.com (My iPad).

  9. Joseph H Murray says :


  10. Joseph H Murray says :

    cancel this is a repeat

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