Galaxy Cluster Abell 1689 Breaks Two World Records

A huge cluster of galaxies so far away that light from it takes 2.2 billion years to reach us has revealed itself to be a record-breaker. It has the largest number of star clusters ever seen in one place and it is farthest place in the universe where we have seen star clusters.

To appreciate this story, you have to distinguish between the two kinds of clusters we're discussing. Stars are often born in groups called "star clusters" and the largest and most impressive of these are called "globular clusters" (because their stars are organized into a big globe-shaped collection of 100,000 stars or more.) Our Milky Way Galaxy has about 150 of these globular clusters and they are among the oldest and most crowded places in our home galaxy.

Galaxies -- the great islands of billions of stars -- also turn out to be organized into clusters. Each cluster might contain hundreds or even thousands of galaxies. (And each galaxy contains billions of stars -- it makes you dizzy if you think too hard about it!)

The late George Abell (an astronomer at UCLA and the author of a famous textbook from which astronomers in my generation first learned astronomy) made a catalog of these galaxy clusters, and the one we are discussing is entry 1689 in his catalog.

A new study of the central region of Abell 1689, made with the Hubble Space Telescope, reveals 10,000 globular clusters of stars in a small region of the galaxy cluster. The astronomers who carried out the work estimate the throughout the entire galaxy cluster, there may be as many 160,000 of these giant old star clusters -- a record unequaled anywhere else we have looked so far.

At a distance of 2.2 billion lightyears, Abell 1689 is also the farthest location in the universe where we have seen a globular cluster.

In the attached picture, you can see part of the cluster of galaxies on the left and then a close-up where the globular clusters look like little yellow dots among the bigger galaxies.

For a scan through the galaxy cluster, you can check out this YouTube video: http://www.youtube.com/watch?v=bumxssc9Cdo
(On this scan, you can also see faint rounded arcs of light -- those are direct proof of one of Einstein's ideas -- that the huge gravity of the galaxy cluster acts like a "gravitational lens" and bends the light of other galaxies behind it into arc like shapes.

We have seen other rich clusters bend light from objects behind them, but the effect is especially clear on this beautifully detailed image. 

A Gorgeous Galaxy Like our Own

We live in an enormous "island" of stars called the Milky Way galaxy -- a collection of over 200 billion stars (and probably billions of planets). Since we are inside the Milky Way, it's hard to take a complete picture of it. It's like trying to take a picture of yourself from inside your gall bladder -- the view is not too clear. But we can learn about our own galaxy by observing others that are like us in size and shape.

In this beautiful picture, assembled from a Hubble Space Telescope image, as well as color information from a Japanese telescope and other observers, you can see a near cousin of the Milky Way located at a distance of about 50 million lightyears. (That means the light from this great "city of stars" took 50 million years to reach us!)

This galaxy doesn't have a name (like most galaxies), but simply referred to by a catalog number -- NGC 7331. Like our Milky Way, it is a spiral-shaped assemblage of stars and cosmic gas and dust. It contains about the same amount of material as our galaxy. We see it tilted to our line of sight, accounting for its oval (rather than circular) appearance.

It appears from other observations that NGC 7331 has a giant black hole at the center that has swallowed much more material than the black hole at the heart of the Milky Way. We are no longer surprised when we find giant black holes at the cores of galaxies -- it appears most grown-up galaxies have them.

Above and to the left of NGC 7331 are two other galaxies, which are about 10 times farther away! They just happen to be in the frame of the picture, like movie extras behind the actor whom our attention is focused on. Billions upon billions of galaxies make up the observable universe.

This gorgeous picture was assembled from different sources by Dr. Robert Gendler, a physician on the East Coast, whose passion is astronomical photography and whose skill at computer rendering of our skies is extra-ordinary. As many students and teachers travel or rest for spring vacation around this time of year, here is a celestial tourist sight for your enjoyment.

POSSIBLE Planet Around a Famous Nearby Star

Today came a news story that illustrates how hard progress is at the very frontiers of science. For both science and science fiction fans, the nearby star Tau Ceti (a sun-like star just 12 lightyears away) is legendary. In science, it was one of the two stars that Frank Drake searched for intelligent signals in his first SETI project back in 1960.  In science fiction, many authors and screenwriters have used Tau Ceti as the home base of alien species.

Naturally, astronomers have searched for planets orbiting this star and no "obvious" planets (such as a big Jupiter-like planet) have been found. A key way astronomers find planets too dim to see with a telescope is to watch the effect of the planet's gravity on the much brighter star. As planets orbit a star, the star will appear to wiggle back and forth slightly, which sophisticated instruments can detect.  (For the technically minded, we can take a spectrum -- spread out the light like a rainbow of colors -- and measure the motion of the star from the Doppler Effect.)

So an international team of astronomers has been analyzing 6000 previous observations of any possible "wiggle" of Tau Ceti from the pull of smaller planets to see if they can tease out any information when they combine the information gathered by three of the largest telescopes in the world, including the giant Keck Telescope in Hawaii. The complex analysis allows scientists to get down to smaller wiggles than have ever been observed before -- down to changes in the speed of the star of 2 miles per hour!

At this level, scientists are down to speeds that are "in the noise" -- smaller than the statistical variations in the observations and the movements of the star's own surface. As the experimenters themselves quickly say, this is new territory. Yet, when they do their best to model and explain the changes in the star's speed, their work is compatible with the possibility that there are five small planets orbiting Tau Ceti. One of these appears to be in the "habitable zone" where life like us may be comfortable.

The discoverers freely admit that it may take a decade to confirm that their tiny wiggles are real. But the possibility of planets around Tau Ceti -- coming so soon after the discovery of a planet around one of the stars in our nearest neighbor star system, Alpha Centauri -- brings new excitement to the idea that planets are going to be found around the majority of stars, even the ones nearby. More than 800 planets are now confirmed out there, and we have thousands of candidates in our catalogs. It's a wonderful universe!

Lecture on "Finding the Next Earth" Now on the Web

With the restart of the Silicon Valley Astronomy Lectures, which I have the privilege of organizing, we are posting the talks on the Web as audio and video. The latest one, on the amazing pla

nets the Kepler mission is finding around other stars, by Kepler Mission Scientist Natalie Batalha, is now available free of charge to everyone.

Podcast: http://astrosociety.org/silicon-valley-astronomy-lectures/

Video (through ITunes U): https://itunes.apple.com/us/itunes-u/silicon-valley-astronomy-lecture/id431445898

It's more than an hour long, with questions at the end, but the speaker is quite non-technical and very dynamic, so I think everyone can enjoy it.  If you know a science teacher or an astronomy buff, please recommend the entire series of these talks, which includes such well known astronomers as Frank Drake (the father of the scientific search for extra-terrestrial intelligence) and Mike Brown (the astronomer who got Pluto kicked out of the planet club). 

Giant Black Hole at the Center of Our Galaxy (and a Video)

A new observatory in space has caught the giant black hole at the center of our home galaxy in the process of having a snack. We know that the at the very heart of the Milky Way there lurks a black hole with as much material inside as 3 - 4 million Suns. When material falls into such a black hole, just before it enters, it gets very hot by friction and gives off (not light but) a glow of x-rays.

Once material falls into a black hole, then no light or x-rays can escape from it. But just before any such stuff goes to its doom, we do see a flare of x-rays from it. It is just this sort of flare that the NuSTAR satellite detected in July (just about a month after it was launched). It wasn't really a full meal for the black hole, merely an afternoon snack, but the temperature of the glowing gas cloud before it fell in was an astounding 180 million degrees Fahrenheit.

The so called "super-massive" black hole at the center of our Galaxy is a relatively small one, compared to some of the really massive black holes in the centers of other galaxies.  Some of these have billions (thousands of millions) of times the mass of our Sun contained within them.

If you are already a black hole fan, such observations will probably just confirm your view of how weird black holes are. But if you are not sure what black holes are, I might recommend a little video that the SETI Institute made of me during a family event there. It's a brief, friendly explanation of just what black holes are and why falling into one is a "once-in-a-lifetime experience." You can see it at:
http://www.youtube.com/watch?v=7DX_cc-IjpY

Extremely Deep View of the Universe

Last month, the Hubble Space Telescope released one of the most impressive astronomical images ever taken and I wanted to share it with you. Called the Hubble Extremely Deep Field, it shows a tiny, tiny portion of the sky in the constellation of Fornax -- a portion about the same size (angle) in our sky as one of the smaller dark splotches (maria) you can see on the Moon.

Between 2002 and 2012, a team of astronomers kept photographing this same bit of sky over and over again for 2 million seconds (almost 23 days) and the results, as you can see, are spectacular. Almost every bit of light you see on the accompanying picture is a galaxy (a collection of millions and, more likely, billions of stars). Some are so far away, light from them is estimated to take 13 billion YEARS to reach us!

This means that when you look at the faintest objects in this picture you are looking almost back to the beginning of time (the Big Bang is estimated to have taken place 13.7 billions years ago.) Some 5,500 galaxies are visible in the small frame of this image and they range in distance and time over billions of lightyears and years. In such images, which are like core samples in geology, astronomers can study the history of structure and matter in the universe.

The Hubble scientists have done this before, taking previous sets of deep images called the Hubble Deep Field and then the Hubble Ultra-deep Field.  But the current image (above) shows by far the deepest view (seeing the faintest galaxies and light from longest ago.)

A Huge and Distant Cluster of Galaxies (and a Movie)

I want to introduce you to a short, but truly mind-boggling movie and then share a piece of news with you. 

All stars are organized into giant islands called galaxies. We live in one 

such island, called the Milky Way Galaxy, and our telescopes show many billions of other galaxies all around the sky. Like explorers on an unknown continent, we have recently been trying to map the way all these galaxies are distributed through space. Perhaps the most impressive such mapping project is called the Sloan Digital Sky Survey, and they just released a short film allowing you to fly through 400,000 galaxies whose positions in three-dimensional space have now been measured. Here is the movie: 
http://www.youtube.com/watch?v=08LBltePDZw 

Note that each little object on your screen is a galaxy of billions of stars (stars like the Sun)! Also note that the galaxies are not evenly distributed. Just like stars, they tend to be "social" -- they collect into groups (or galaxy clusters). 

Just today, astronomers announced the discovery of one of the largest galaxy clusters ever seen, nicknamed the Phoenix Cluster. It contains enough material (in many many galaxies) to make more than 2 million billion Suns. And it is almost 6 billion light years away, which means the light we see tonight from this huge grouping of galaxies left on its way to us before the Sun and the Earth ever existed. Wow. 


What makes the Phoenix cluster of special interest to astronomers is that, at its center, the gas falling in from all over the cluster is leading to a huge rash of newly forming stars. 740 new stars form in the middle galaxy of the cluster EVERY SINGLE YEAR. Many such galaxy cluster have a core that is "red and dead" -- with little star formation going on in the central galaxy. But this cluster has a center that's "blue and new" -- with lots of new stars being born. 

You can just stop there if (like many people) your head now hurts from the movie and the huge numbers I am throwing around. Just let the feeling of the immensity of the cosmos overtake you. (It helps a lot when you can't stand the pettiness of presidential politics these days.) Or, for more on the Phoenix Cluster see:

http://chandra.harvard.edu/press/12_releases/press_081512.html
or
http://www.skyandtelescope.com/news/Heavyweight-Cluster-166282866.html