Marusa Bradac: I do astronomy because it fascinates me. And it is the simplest things about it that amaze me most. I still remember times when I was a little girl watching stars with my dad in my home country Slovenia and wondering, "how far away are they?" I also remember how exciting it was when I first saw the Andromeda galaxy in our backyard. These days I moved on to much bigger things called clusters of galaxies. But the excitement of the question of how far away they really are is still there.

Illustration of our Solar System
Illustration of our Solar System

Do you still remember those models of the Solar System that teachers showed you in school (where nothing was really to scale) that were so cool? Now take our Solar System, including Pluto (remember, even though not a planet anymore, it still belongs to the Solar System) and squish it to the thickness of your hair, approximately one hundredth of a millimeter. Then the next closest star, Proxima Centauri will be a meter away. And the closest galaxy to our galaxy is already 250 miles away. In fact, it is so far, that it takes the light more than 2 million years to travel to us. Further even is the closest galaxy cluster, called the Virgo Cluster, where the light we see today left it 60 million years ago. On our scale it would be already 6000 miles away from us (a distance from Santa Barbara to a tiny country where this story really started, Slovenia).

The galaxy cluster I'm most interested in these days, MACS J0025.4-1222 is even much further. The photons we are observing with Chandra and the Hubble space telescope took 6 billion years to travel to us. And since the light left it, the cluster moved even further away from us. In our model, the cluster is now at three times the distance to the Moon! And remember, we started with a hair.

Macs J0025
Galaxy Cluster MACS J0025.4-1222

And as if this isn't enough, the cluster is actually made of two clusters that have smashed together with 5 million miles per hour. So the Universe has provided us with a cosmic accelerator. And when we weigh the cluster, it turns out that what we see is not at all what we get. We get six times more mass than we expect based on what we detect, and that “more” is dark matter. This cosmic accelerator has allowed us to study the properties of this dark matter, quite similarly to the giant collider Large Hadron Collider (LHC) built at CERN that will soon turn on. So we can say already that dark matter is, simply speaking, weird. Or anti-social. It doesn't like to play with anyone, not even photons. The only reason why we know it is there, is because it has mass and it attracts photons through gravity, altering their path as they travel, which is the effect we call gravitational lensing. But it doesn't absorb photons like your dark T-shirt does (and you know it does, because it gets hot on a summer day). Dark matter is not just dark, it is invisible. And it is all around us. If the physicists have guessed its particle mass right (and LHC will give us an answer to that) there are few dark matter particles in an average class room. Here and in Slovenia. Now if this is not fascinating!

Illustration of Gravitational Lensing
Illustration of Gravitational Lensing

Marusa Bradac is a postdoctoral researcher at the University of California Santa Barbara, and she’s also a Hubble fellow. Her main research interests include studying dark matter in galaxy clusters, figuring out gravitational lensing, and exploring the very distant Universe.

Average: 5 (1 vote)

great article man...

Considerably, this article is really the sweetest on this notable topic. I harmonise with your conclusions and will thirstily look forward to your incoming updates. Saying thanks will not just be sufficient, for the phenomenal clarity in your writing. I will directly grab your rss feed to stay informed of any updates. Admirable work and much success in your business dealings! Please excuse my poor English as it is not my first tongue.


Thanks for sharing this!

Thanks for sharing this! Will you believe that even the outer space is experiencing recession? Here’s the thing: The commercial space travel is slowing down. Companies like Roskosmos and Space Adventures travel companies, have been seeing less business and now they can't book any more flights to the International Space Station because actual space agencies are using it. A flight through these companies costs more than any payday loan will cover, as it is in the dozens of millions to get booked. Turns out even the largest of a no fax cash advance doesn't matter in outer space.

I do astronomy because it fascinates me

I always liked astronomy. Since childhood my father would take me outside late in the night when the sky was clear to show me the stars and constellations. It was something so exotic and fascinating for me. Nowadays I practice a totally difference specialty. However, my passion for astronomy is still at it's highest peak and I feel like a small child when looking at the stars. Stumbling upon your blog offered me hope to continue my astronomy studies.


Its also my ultimate fascination

I am not an astronomer nor am I an astronomy student. I am a teacher by profession and as I am reading this now, it brings back moments in my life since childhood when I would be staying outside or on our rooftop just gazing at the stars. I would love darker nights or when the whole town is having blackout because it would mean that the stars would be even clearer and more. I haven't even tried using a telescope to see them clearer, but I am satisfied just watching them afar as they twinkle. There's just something with their spark in a dark sky.

Disclaimer: This service is provided as a free forum for registered users. Users' comments do not reflect the views of the Chandra X-ray Center and the Harvard-Smithsonian Center for Astrophysics.
Please note this is a moderated blog. No pornography, spam, profanity or discriminatory remarks are allowed. No personal attacks are allowed. Users should stay on topic to keep it relevant for the readers.
Read the privacy statement