Hubble spots 67 gravitational lenses

By Phil Plait | February 19, 2008 7:01 am

Gravitational lensing is all the rage these days! The fact that massive objects have gravity that bends lights was a prediction by Einstein, but it has come into its own over the past few years as a way of learning more about the Universe. We’ve used it to map dark matter, and to find planets orbiting other stars. The more lenses we find, the better we can map out the distant Universe.

And now Hubble has found new ones. 67 of them, in fact!

Gravity bends the path light takes in a similar manner in which a car has to follow a dip in the road. Gravity warps space, and a beam of light follows that warp. Galaxies have lot of mass, and therefore a lot of gravity. Imagine a distant galaxy, billions of light years away. Between us and it is another galaxy, much closer to us. The distant galaxy is sending out light in all directions. Light that happens to be aimed at us will eventually reach our telescopes.

But now imagine a beam of light that just misses us. It’s not quite aimed right at us. However, the galaxy in the middle bends the path of that beam, angling it just enough to hit us. Light from the distant galaxy that would otherwise miss us can hit us due to the lensing action of the galaxy in the middle! That makes the distant galaxy brighter to us: we’re getting more light from it.

But it also distorts the shape we see for that distant galaxy. It can be stretched out into arcs, for example, if the intervening galaxy is off to the side a bit. Like this:

Back when I worked on Hubble, one of our Early Release Observations (cool pictures taken right after a new camera is checked out) was of a cluster of galaxies — think of it as a condominium of galaxies — surrounded by four separate arcs. When I put the images together into a mosaic, I just stared at it. I had seen lenses before, in books and such, but never on data that I had personally been working on. That was very nifty.

But it gets better. If the lensing galaxy is smack dab between us and the farther object, the light can be focused into a perfect circle, called an Einstein Ring. The first image above is one of those. They’re pretty. They’re also terrifically cool.

We can learn a lot from such lensing. For one, we can see distant galaxies that might otherwise be invisible. Sure, they’re all twisted and weird, but we can still investigate them: spectra can tell us if stars are forming, for example. Also, the amount of distortion can yield the mass of the lensing galaxy (since the amount of lensing depends on the lensing galaxy’s gravity, which itself depends on the galaxy’s mass) and that can even be used to map out dark matter.

So this is pretty interesting news, and worth poking over the images. Certainly they are scientifically useful, but images of lensing events are also pretty weird. Looking at them is a reminder that the Universe is a pretty strange place.


Comments (13)

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  1. Astronomy Pictures - Images of moon | February 20, 2008
  1. bob allee
  2. TomR

    Very cool. It’s amazing, I can still remember when the first one of these was found, and now they’re turning out to be as common as naked-eye stars. Nice piece of kit, that Hubble.

    Anyone know the apparant magnitude of these? I imagine they’re out of reach for most amatur astronmers, but it would be fun to try and spot one.

  3. Why was the TAU project called off?

    Thousand Astronomical Unit – send a powerful hubble – NGST probe to 1000 AU and use the sun as the primary lens in a giant refractor telescope. Yes it would call for blocking the sun’s light carefully. Anyone know more about this?

  4. Phil…

    Have redshift measurements been carried out on any of the 67 lensed objects? It would be interesting to see the difference between the measurements of the lensed object versus the lensing object, especially on the Einstein ring shot.


  5. Gary

    How do astronomers separate the light from the object galaxy and the gravitationally-lensing galaxy when they and we are aligned directly?

  6. Jeffersonian

    Thanx. (The gravitational bending of distant light has always been an enthusing subject for me but actually grappling with the corollary implications has been elusive. That’s why I appreciate post like this.)

  7. On the subject of Robert Heinlein quotes, try this one:

    “The hardest part about gaining any new idea is sweeping out the false idea occupying that niche. As long as that niche is occupied, evidence and proof and logical demonstration get nowhere. But once the niche is emptied of the wrong idea that has been filling it – once you can honestly say, ‘I don’t know,’ then it becomes possible to get at the truth.”

    That’s the one thing most fundamentalists can’t seem to say. They always KNOW, don’t they?

  8. By the way, I haven’t watched that video. The comments above are enough to put me off. I don’t want to destroy any brain cells unneccesarily!

  9. hale_bopp

    If you have a large telescope, there are at least two gravitational lenses I have seen visually. Both of them were on the same crystal clear night with a 22″ telescope in a freakishly dark location.

    There is a twin quasar in Ursa Major at ra 10 01.3 dec+55 54. You need good seeing for this one.

    Even tougher, is Einsteins’s Cross at ra 22 40.5 dec +03 21. This one is REALLY TOUGH! We did get it, but only try it with a big scope on an excellent night from a really dark site!

    I use it as an example of the wonder of science. If you don’t know what you are looking at, the reaction is likely to be “Is that it?” if they see it at all. If you KNOW what you are looking at, these barely visible smudges at the edge of our vision inspires goose bumps. I literally was choked up, knowing that the quasar was 8 BILLION LIGHT YEARS AWAY and the light I was seeing was created before the Earth. When some yahoo tells me that studying science somehow detracts from your appreciation of natural beauty, I just want to smack ’em upside the head!

    If anyone wants a great list of deep sky objects, I recommend The List put together by a friend of mine in Bradenton. It contains what he considers the best 400 deep sky objects (including the two gravitational lenses listed here) arranged by ra. It can be downloaded from the Local Group of Deek Sky Observer’s web site at

  10. Gary Ansorge

    If space near a rotating black whole is stretched, wouldn’t that appear(from the point of view of matter trapped in that distorting space/time) as though the space was expanding, as it appears to us when we look back nine billion years?

    Just a (slightly) off topic thought,,,


  11. Steve P.

    Unfortunately it seems the mosaic image (Fig. 2) from your paper isn’t appearing.

  12. Tom Marking

    “Why was the TAU project called off?


    All I can find on TAU is a very old article from 1987 talking about it. I don’t know why it never went anywhere. Maybe it had to do with the very long time to get the spacecraft out to 1,000 AU. On the other hand it could be doing observations all the way out. You never hear about anymore so I’m assuming it’s dead as far as NASA is concerned. I think it was a good idea. Imagine, increasing our distance precisions to nearby stars by a factor of 500 and getting the first reliable distances to remote objects such as the Orion Nebula. It would have been good stuff.


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