So Do Twin Quasars Exist or Not?

Who was going to tell me that space just gets weirder and weirder and … well more mischevious!

In the middle are the twin quasars! Credit to NASA and ESA.

The Twin Quasar, also know as the Double Quasar or SBS0957+561 is a … wait a minute. That fancy numerical name only has one coordinate, where are the coordinates for the second quasar?

We’ve been bamboozled! It’s actually only a single quasar!

A Quick Recap on Gravitational Lensing

One of Einstein’s predictions from General Relativity, gravitational lensing is an awesome phenomenon where light behind a very massive object is distorted around it.

Galaxy cluster SDSS J1038+4849. Credit: NASA/ESA/Hubble Wide Field Camera 3.

You might think aw shucks! The galaxies behind are all messed up! How are we supposed to look at them!? But not only is the light distorted, but it’s also magnified! So these objects that are normally too far away to be observed are suddenly all that bigger and better!

In the most massively-dense cases, distant galaxies can bend all the way around an object and form a beautiful ring commonly called an Einstein ring!

This topic will get covered in more detail some time soon.

So What’s Going on With the Quasar?

Twin Quasar taken with 2MASS, from SIMBAD/NED/NASA

When these quasars were discovered, astronomers already recognised that it could be just one object distorted to look like two. They’re already extremely close to each other, about 6 arcseconds apart, and had the same redshifts and very similar apparent magnitudes.

The team that discovered the quasar suggested it could be an example gravitationally lensing, and actually it would have been the first piece of evidence for lensing ever! This is a substantial and bold claim, even Einstein himself didn’t think we’d be able to see lensing!

Twin Quasar using DSS Catalogue. From SIMBAD

At the time, other astronomers recognised that the quasars are spaced apart by a lot, too much to be accounted for by gravitational lensing. 6 arcseconds sounds small (and to be fair it is small!) but these quasars are 8.7 billion light years away. Those 6 acrseconds are a great distance in this context. Secondly, at the time of discovery we could see only 1 of the quasars had a relativistic jet. It didn’t seem like they’re completely identical.

But we’ve missed one critical piece of the puzzle: The galaxy distorting the quasar. G1, the massive galaxy in front of the quasar, is part of a large galaxy cluster. This means we not only have the galaxy’s gravity but some “gravitational support” from the rest of the cluster, all of which can account for the 6 arcsecond separation!

Twin Quasar from SDSS Catalogue from SIMBAD.

Techniques such as Very-Long-Baseline-Interferometry helped astronomers identify an identical relativistic jet in the imaged quasar. These radio jets are extremely long, so the issue may have been that not all of the jet is in the right spot for lensing.

Astronomers were able to prove the quasar was lensed by G1, and it became the first piece of evidence for gravitational lensing!

Extra Reading

Despite being only one quasar, sometimes it is referred to in the plural. It is more appropriate to use singular pronouns, but you can do whatever you want!

Have a look around on SIMBAD, it has much more numerical information on galaxy G1 and a couple images too. I used the 2MASS, DSS, and SDSS catalogues to look at images of the twin quasar. These images are dotted around the post, and the main quasar is marked with a green cross.

PanSTARRS’s Twin Quasar, screenshot taken from AladinLite.

I also used Aladin to look at the twin quasar using the PanSTARRS catalogue. Have a look at Chandra, XMM, and all the other catalogues. It’s so much fun! Remember to put SBS0957+561 into the search!

Let me know of any odd astronomical objects and I’d be more than happy to write about them!


  1. “… even Einstein himself didn’t think we’d be able to see lensing!”

    It always amuses me how Einstein didn’t appreciate the full implications of his own work. He didn’t think we’d ever find black holes or gravitational waves either. He knew these things were mathematically possible, but he thought they were too extreme to actually exist in nature.

    Liked by 1 person

    • I completely agree with you! He is sort of correct; I mean, it was only the last decade that we finally saw M87, a black hole, in all its glory! Before then we never actually had an image of one. Plus, we’re only just getting the equipment precise enough to see gravitational waves. It took a fair few failed attempts for us to realise how large our detectors need to be! I really wish he could have been with us in the 2010s, to see how far we’ve come!

      Liked by 1 person

        • Ah well you can’t have everything! I think he’d let it slide, as I remember he was quite humble when Hubble (and his assistant) proved expansion. He’d just be grateful of our advances!

          Liked by 1 person

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