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Astronomy Firehose: Day 2 of Exploring the Universe from Florida

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Astronomy Thought-provokers

The universe is filled with interesting objects that tell some of the most fascinating stories in astronomy. Today, among other topics, we heard about weird x-ray objects and the possibility of searching out civilizations in globular clusters. If anybody in Hollywood needs a writer to cover those ideas for the next galaxy-spanning Sci-Fi epic, I’m your person!

The Andromeda Galaxy’s X-ray Binaries

astronomy news: scientists find x-ray binaries in the Andromeda Galaxy
At approximately 2.5 million light-years away, the Andromeda Galaxy, or M31, is our Milky Way’s largest galactic neighbor. The entire galaxy spans 260,000 light-years across – a distance so large, it took 10 GALEX images stitched together to produce this view of the galaxy next door.
The wisps of blue making up the galaxy’s spiral arms are neighborhoods that harbor hot, young, massive stars. Meanwhile, the central orange-white ball reveals a congregation of cooler, old stars that formed long ago.
Andromeda is so bright and close by that it is one of only three galaxies that can be spotted from Earth with the naked eye. This view is two-color composite, where blue represents far-ultraviolet light, and red is near-ultraviolet light.

So, what happens when an object sends out lots of x-ray radiation? Obviously, it catches the attention of astronomers because it’s very likely telling us that something fascinating is happening. X-rays are generated in very hot, active environments, such as near black holes or in the explosions of massive stars. Our Sun also gives off x-rays, particularly as it generates strong outbursts called flares.

Our galaxy — and many others — has a collection of objects called x-ray binaries. Each one contains a black hole or a neutron star accompanied by a stellar companion. These pairs give off prodigious amounts of x-rays.

Astronomers looked at the nearest spiral galaxy to us — called the Andromeda Galaxy — and 40 of its x-ray binaries. They used the Nuclear Spectroscopic Telescope Array, or NuSTAR, to study them and figure out what role they played in early galaxy formation. Some researchers suspect that these objects could have been responsible for heating up intergalactic gas clouds in the early universe. The idea is to study these x-ray binaries in a “nearby” galaxy and then apply what we learn about them to similar objects that existed when the universe was very young.

In x-ray binaries, material from the companion star can “spill over” and then be captured by the strong gravitational pull of the nearby black hole or neutron star. That material gets heated to incredibly high temperatures, and the result is an intense release of x-rays.

NuSTAR looked at a swath of Andromeda, which revealed the 40 binaries. Now astronomers are working on identifying which ones may have black holes and which are powered by neutron stars. These remnants of stellar evolution and their companion stars may have played a very central part in heating the early universe.

Life in a Crowded Stellar Suburb

astronomers think about planets in globular clusters.
Are there planets orbiting the stars of this globular cluster? If so, could there be a thriving interstellar civilization there? Recent studies at Harvard are exploring those possibilities. Courtesy STScI.

As you probably know, astronomers have been finding planets around other stars for a few decades now. The big question — do they bear life? — is the question that is, so far, unanswered. At least one of those planets has been found in a globular cluster, which is a collection of a million (or more) stars packed into an area of space about 100 light-years across. That led astronomer Rosanne DiStefano of Harvard-Smithsonian Center for Astrophysics to wonder whether more planets might exist in globular clusters. And, since she was engaging in “what if” scenarios, she speculated about what civilizations could exist on those planets.

“A globular cluster might be the first place in which intelligent life is identified in our galaxy,” she said today.

Globular Clusters? Really?

At first glance, globular clusters don’t seem like great places to grow planets. They’re old — they formed about 10 billion years ago. Their stars contain fewer of the heavy elements needed to make planets. Those elements (like iron and silicon) are created in earlier generations of stars. Some scientists have argued that this makes globular cluster stars less likely to host planets. However, DiStefano and Alak Ray (Tata Institute of Fundamental Research, Mumbai) think that view is much too negative.  “It’s premature to say there are no planets in globular clusters,” Ray said.

If you look at a globular cluster, it seems like it would be too crowded to allow planets to exist in stable orbits around their stars. However, it turns out that if a star’s habitable zone is close enough in, a planet could exist in a reasonably stable orbit. And, if it’s an Earth-like planet around an older, cooler star, that zone would be pretty close.

Here’s another thing about those clusters. Since they are old, their most massive stars have died off, leaving behind the older, cooler stars — and a supply of heavier elements that could be useful in planet formation.

So, it does seem possible that habitable planets can form in globular clusters and survive for billions of years. Take the next step and endow them with civilizations, and you have a whole new set of thoughts to consider about the possibilities for life on them, and what globular cluster civilizations would be like.

Such a civilization would enjoy a very different environment than our own. The nearest stellar neighbors would be just a trillion miles away, That would make interstellar communication and exploration quite easy, compared to what we have to do here on Earth to talk to the neighbors.

“We call it the ‘globular cluster opportunity,'” said DiStefano. “Sending a broadcast between the stars wouldn’t take any longer than a letter from the U.S. to Europe in the 18th century.”

“Interstellar travel would take less time too. The Voyager probes are 100 billion miles from Earth, or one-tenth as far as it would take to reach the closest star if we lived in a globular cluster. That means sending an interstellar probe is something a civilization at our technological level could do in a globular cluster,” she said.

The closest globular cluster to Earth is several thousand light-years away, making it difficult to find planets from our vantage point. It’s a big problem in the core of a cluster. That’s because the stars there are really jammed in together. But, it could be possible to detect planets on the outskirts of globular clusters. Astronomers might even spot free-floating planets by using applications of gravitational lensing. That occurs when the planet’s gravity magnifies light from a background star.

A more intriguing idea might be to target globular clusters with SETI search methods, looking for radio or laser broadcasts. That concept has a long history: the late astronomer Frank Drake used the Arecibo radio telescope in 1974 to broadcast the first deliberate message from Earth to the globular cluster Messier 13 (M13).

Okay, so we don’t KNOW if there are planets and civilizations in globulars, yet. But, DiStafano and her colleagues have raised some cool things to think about as we look for exoplanets in our galaxy — and beyond. THAT is one of the great attractions of astronomy!

AAS meeting stories, american astronomical society, andromeda galaxy, astronomy, astronomy news, cepheid variables, Hubble Space Telecope, stars, stellar distances

Hubble’s Star

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How A Star Expanded Our Understanding of the Universe

Humans have stared at the stars throughout history and that makes stargazing one of our oldest sciences. Probably THE oldest, along with the accidental chemical experiments that led our earliest ancestors to create things like soap and tea and other necessities.  And, of course, humans have engaged in biological experiments throughout history, and eventually took up engineering and geology and all the other sciences we know of today.

Still, it’s astronomy that piques our interest. I often think about what the first people who stared at the stars thought of what they were seeing.

I’ll give our species the benefit of the doubt and assume that there was intent curiosity about it all, a sense of wondering what they are and if they could be touched or visited. It probably didn’t take long for humans to start woolgathering all kinds of stories about them, and eventually their awe at these sparkly things turned into some kind of reverence.  Heck, a sunrise inspires me greatly, and I’m sure it did for those early folks, as well.

I also like to think of those early astronomers getting together and discussing what they saw, debating what the motions meant, how they were made, and what relationship those things had to Earth. The history of astronomy is written by those people who did MORE than just look at the sky.  They made careful notes about what they saw, and those observations led to speculation and eventually the application of scientific principles to explain the structure and motions of things in the sky. And, in due time, they shared their knowledge and our societies are richer for it today.

Speaking of meetings, the summer meeting of the American Astronomical Society is taking place this week in Boston. I can’t be at this one, but I’m hearing and seeing lots of fascinating news from the assembled astronomers.  They’re sharing what they’ve found — from planetary systems to peeks at the most distant stars and galaxies.

The star that changed our perceptions of distance in the universe. Courtesy STScI.

One story that caught my attention is focused on a star in a distant galaxy. It first caught the attention of an astronomer early in the 20th century. The star is a Cepheid variable star — that is, one that pulsates in brightness in a regular and predictable rhythm. It caught the attention of astronomer Edwin Hubble (for whom the Hubble Space Telescope is named).

He knew that the light pulsations could be used to help measure distances in the universe. So, he did what any self-respecting astronomer would do, he measured the pulsations precisely, kept good records, and when he had enough good data, he calculated the distance to the star.

That calculation (which any student in astronomy can do these days), showed that the galaxy in which the star existed — the Andromeda Galaxy — was not part of the Milky Way Galaxy that we live in.  It wasn’t even close. Instead, it and Andromeda were at least 2 million light-years away.

This finding probably excited Hubble very much; enough that he sent a letter to his colleague, Harlow Shapley, describing his finding. Shapley recognized the significance of Hubble’s finding — that is, that the universe was larger than we thought — and commented to another colleague, “Here’s the letter that destroyed my universe.”

It was an important step in understanding how large the universe is, one that astronomers still rely on today to figure out distances to some of the farthest objects in the cosmos. In commemoration of Hubble’s  landmark observation, astronomers with the Space Telescope Science Institute’s Hubble Heritage Project partnered with the American Association of Variable Star Observers (AAVSO) to study the star.  AAVSO is a group of dedicated observers (both amateur and professional) who focus on the glimmerings of variable stars. Their work has contributed greatly to our understanding of these stars — and hence, to distances in the cosmos.

AAVSO observers followed brightness pulsations of the star in Andromeda — called V1 — for six months. Their observations were combined into what astronomers call a data “plot” (that is, put into an X/Y axis, just like you might remember doing in geometry or calculus). That plot is called a “light curve” and it shows  the rhythmic rise and fall of the star’s light. (If you want to see what a light curve looks like, click on the AAVSO link above; they have some on their front page, and explain them in more detail).

Based on this data, the Hubble Heritage team scheduled Hubble telescope time to capture Wide Field Camera 3 images of the star at its dimmest and brightest light levels.

As a reminder of how important these observations are, the combined data and images were presented at the AAS meeting on Monday (you can read the whole story here). Astronomer Max Mutchler commented, “This observation is a reminder that Cepheid variables are still relevant today. Astronomers are using them to measure distances to galaxies much farther away than Andromeda. They are the first rung on what astronomers call the cosmic distance ladder.”

That ladder stretches out to the earliest stars and galaxies, more than 13 billion light-years away. It’s an awesome achievement for a species that only began looking at the stars with the intent to understand them perhaps a few hundred thousand years ago.