Black hole menu

It is a depressing fact that over 95% of the Universe can't be bothered to interact with you. By looking at the speed with which our galaxy is rotating, we can infer that the amount of mass present must greatly exceed what we can see in stars and gas. This 'dark matter halo' is the cocoon in which our brightly lit spiral galaxy lives.

One of the puzzling features of these galactic cocoons is their wide range of sizes. It is surprising because the size of a galaxy is proportional to its dark matter halo, yet there are no galaxies found in very small or very large halos. It's a little like looking at the cities in Ontario, and finding everyone lives in Hamilton or London, but there is not a soul to be found in Toronto or Ancaster. Additionally, the large galaxies that do exist tend to have predominantly old stars, with very little cold gas from which new stars could form. So, in our Ontario analogy, Ottawa would be populated only by people over the age of 65.

The absence of small galaxies in small halos is explainable by the violent deaths of stars. As a star such as our sun reaches the end of its life, it will throw a large fraction of its substance into the surrounding area in an explosion called a supernova. In a small galaxy, this can blow so much gas out of the halo cocoon that it destroys the galaxy, leaving behind a star-less dark matter halo.

The absence of very large galaxies in the biggest halos however, is more of a mystery. The amount of mass in these galaxies would be so large that any gas that is ejected away from the disc by supernovae will be dragged back down by the gravitational pull of the remaining matter. In the last Origins talk of the semester, Professor Tim Heckmen from John Hopkins University in Baltimore proposed that the answer lies with super-massive black holes.

The most sinister objects in the Universe, a black hole is where so much mass has been squeezed into such a tiny volume that the speed needed to escape its gravitational pull is greater than the speed of light (and that's the fastest speed there is!). For the Earth to become a black hole, it would have to be compressed down to the size of a grape. Super-massive black holes containing the mass of billions of suns, reside at the centre of galaxies. How they have formed is hotly debated but what is known is that the larger the galaxy, the larger its super-massive black hole. Of course, something that destroys everything that enters it does not have the best PR, so going to these objects for answers feels like asking a kraken to attack a single ship; the probability of having any vessels left at the end of its foraging seems rather low.

Professor Heckman's theory is that gas close to the black hole is pulled towards it like water swirling down a drain. As it approaches the edge of the hole, the energy the gas is loosing (by dropping down the black hole-drain) is converted into heat at a rate that is much more efficient than nuclear fusion. The resulting radiation is the most intense source in the Universe. If enough gas falls in, the black hole can go through a 'feeding frenzy' and produce jets that evacuate huge holes in the galaxy. These jets fill the halo with hot gas, removing all the cold star-forming gas from the disc. If the jets are strong enough, the galaxy could be destroyed completely. If it isn't, then the resulting cavity around the black hole removes its food supply and the jets turn off. Yet, as the ejected gas cools, it falls back down to the galaxy, serving up another black hole dinner.

Why though, would this mechanism not occur in our own Milky Way, destroying us and smaller galaxies along with the bigger ones, kraken style? The answer, Professor Heckman explains, is that the super-massive black hole needs feeding with a lot of gas to produce the powerful jets. One possible source of this food is from supernovae as they blow away their outer layers. This gas might initially go into the halo, but as it returns to the galaxy, it could be drawn into the black hole which would then start to feed and produce jets. Larger galaxies will have more stars and therefore more supernovae, increasing the food supply to a point where jets can be formed. This means that the lifecycle and star production of a galaxy is intimately linked to its super-massive black hole. To understand one, Professor Heckman said, you need to understand the other.

At the end of the talk, there was one important question on the audience's mind:

Which came first; the black hole or the galaxy?

A picture is worth a 1000 words

While at a conference in Italy in 2009, I attended a talk on new observations of a nearby spiral galaxy. The speaker presented several interesting results but had to confess she did not have an image of the galaxy, since they were still waiting for data from the Hubble Space Telescope. From across the room of eminent astronomers came a collective sigh of disappointment.

It was hard not to laugh. In fact, I don't think I succeeded. The idea that professionals in the field would bemoan the lack of a pretty picture was deeply amusing; surely we should all be above requiring such frivolities? 

The truth, however, is that visualisation is an intricate part of successful science. Presenting your data in such a way that the main results stand out makes for better communication, without which scientific ideas cannot be shared, tested or accepted. This was the concept behind the "Science Illustrated" conference in Toronto that Masters student, Mikhail Klassen, attended last month and was badgered into talking about at the department's weekly journal club.

Mikhail explained that the conference discussed how the way you present your results can both help and hinder the viewer. Consider, for instance, the block of letters in the image at the top of the page. If you were asked to count the number of occurrences of the letter 'v', it would take you at least a few minutes to carefully examine each line. If instead each 'v' was coloured red, the task becomes a matter of seconds. A more extreme example is that of Anscombe's Quartet which is shown in the bottom half of the image. These four data sets have statistically identical properties, including exactly the same average and spread. If these were actual scientific measurements, a glance down the columns might cause you to think that they were showing the same result. However, if you plot them on a graph, you can see at once that they show completely different trends.

On the other hand, you can also choose to visualise data in a way that confuses the viewer. A famous example of this was a power point slide showing the current situation in Afghanistan. So crowded with interlinked lines was this plot, that General Stanley McChrystal, the US and NATO force commander, remarked dryly:

"When we understand that slide, we’ll have won the war."

A common error, if slightly less extreme than the above example, is to pick a bad colour scheme. Using colours that are similar to one another can obscure the trends you are trying to illustrate. Our brains also have a 'perception priority' when dealing with visual input, placing relative position above colour. This means that if an important result is, for example, the maximum density in your galaxy, it could be that plotting this on a line graph is more effective that colouring an image of the galaxy by density.

Mikhail went on to point out that there is also an ethical side to data presentation. By plotting two quantities against one another to demonstrate a relationship, you are excluding any information about other, possibly important, factors. A non-astrophysical example of this is a reconstruction of the Air France flight 358 that crashed in Toronto in 2005. From a reconstruction of the plane landing, it appears to be a pilot mistake; the plane drifts, touches down too late on the runway and over-shoots to crash into the creek (no fatalities). However, there is no weather information in the movie and eye witnesses report strong rain and winds with terrible visibility. As scientists, it is our duty to state clearly what is and isn't shown in our plots to ensure we do not mislead our audience.

Mikhail's final point from the conference was to remind us that communication of results depends on our audience. If we are presenting our findings to the public, we will be competing with Lady Gaga for their attention! This might lead us to choose difference visualisation techniques than if we were presenting to other astrophysicists. Although, if my experiences in Italy were anything to go by, that isn't necessarily the case.

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[Thanks to Mikhail for sharing his (very clear!) slides from his presentation. The bottom right image showing plots from Anscombe's Quartet was taken from wikipedia.]

Sneaky little hobbitses

Despite what you may have claimed over coffee this morning, 18 million years of evolution separates your landlord from a gibbon. If it's any consolation, he's only about 5 million years from a chimpanzee. After that time, our own branch of the tree-of-life evolves through a series of distinct 'hominids' before producing grad students.

But who were our ancestors and what did they look like? Is it possible to distinguish them from other branches of the ape family tree?

This was the topic of today's Origins Seminar, given by Dr Dean Falk from the School for Advanced Research in Sante Fe, New Mexico. Dr Falk is what is referred to as a 'paleoneurologist', a peculiar sounding term for someone who studies fossilized brains. Ancient remains of mammals can have a cast of their brain (known as an 'endocast') preserved via sand and other debris filling the cavity between skull and tissue. This hard coating is protected from weathering by the fossilised skull which slowly wears away, leaving the natural endocast in its wake.

The process of analysing an endocast is not an easy one since it is only an imprint of the brain's surface, so no internal information regarding the neurons or chemical structure is preserved. However, by comparing endocasts from humans and apes with those from ancient remains, much can be learnt about our own evolution.

Of course, it does help if the ancient remains you are studying are not fake. A famous example of this situation is the "Piltdown Man". Discovered in the UK in 1912 in Piltdown, East Sussex, these fossilised remains were exposed as a forgery in 1953. Rather than being the missing link between humans and chimpanzees, this skeleton was created from a human skull attached to an orangutan's jaw. The teeth had been filed down and the bones stained to look like a single specimen. In part, its success as a hoax was due to it fitting in with the preconceived idea that a measure of evolution was the brain-case size; the prevailing belief was that brains became bigger first and the rest of the body, including the jaw, changed afterwards. The discovery was also pleasing to local scientists who embraced the idea that the first human was an Englishman!

In reality, however, the first hominids were found in Africa. Ten years after the 'discovery' of Piltdown Man, Raymond Arthur Dart discovered the remains of the 'Taung Child' in South Africa; a fossil dating back 2-3 million years. With its small ape-sized brain and location far from England, the Taung Child contradicted everything seen in the Piltdown Man, making it a controversial discovery. Dart examined the brain endocast and concluded that, while the brain was relatively small, it was advanced due to its structure. In particular, he identified two groves whose positions matched those found in humans but not in apes.

Ultimately, Dart's analysis was proved to only be partially right, but the technique of examining the position of the brain's major groves (sulcal patterns) is the main way of differentiating hominid brains from our ape cousins. These differences come about as regions of the brain that were previously separated become more interconnected in humans.

Interestingly, our own ancestors were not the only bipedal species walking around Africa 300 million years ago. Paranthropus are thought to be an extinct hominid species, unrelated to us. Their brains were characterised by a prominent central ridge from which strong jaw muscles would have been attached. Our relatives were the Australopithecus africanus, of which the Taung Child is an example. The migration and spread of A. africanus is thought to be north out of Africa and then into Europe and Asia. This has been called into question recently, however, by the discovery of a hobbit.

The announcement of the three feet tall hominid remains found in Indonesia came in 2004. The attractively named, "Lb1" was female with very short legs and therefore seemingly disproportionate long arms. Her feet were genuinely long, stretching a length equal to the distance between her knee and ankle. The remains were found with primative tools, similar to those found in Africa, and she would have lived alongside giant Komodo dragons, which is a slightly unnerving prospect for someone only three foot high.

At 417 cubic centimetres, Lb1's brain was chimp sized but the endocast revealed advanced features reminiscent of a human over an ape. Her discovery opens many questions, with schools of thought differing over whether Lb1 can be a new human species from our ancestry when her brain is small and she was found so far from the picture of migration out of Africa.

One thing that appears to be clear from the endocast discoveries is that brain evolution can occur in many different ways. It is possible to rewire and reorganise our grey matter without it becoming larger. This leads to different combinations throughout the fossil history; a difficult challenge to place in logical order. So in short, size does matter, but it's not just about how much you've got. It's what you're doing with it that counts.

Can you build a transmitter?

"You claim that there are many Earth-like planets while finding none!"

"But we have found many Jupiter-sized planets and they should be rarer than Earth-sized so the trend is pointing towards a large number!"

I was sitting in the audience of "The Great Extraterrestrial Debate", an event hosted by the Centre for Inquiry in Toronto. It was part of the organisation's "Extraordinary Claims" campaign which is designed to put some of today's most controversial allegations through a critical examination. This evening's topic surrounded the likelihood of alien life interacting with us on Earth.

The debate comprised of a panel of three individuals whose profession gave them a stake in this field. The first was Astrophysics Professor, Ray Jayawardhana, from the University of Toronto, whose research focusses on planetary formation outside our Solar System. The second was science fiction author, Robert J. Sawyer, and the third was Seth Shostak, a senior astronomer at S.E.T.I. (Search for Extraterrestrial Intelligence) Institute.

Despite being labelled a 'debate', it was stated upfront that all three panellists were in agreement; to this date, there has been no strong evidence for life outside of Earth. That said, the three unique view points being brought to the table did lead to passionate discussion. The above snippet was between Ray Jayawardhana and Robert J. Sawyer and was wrapped-up by Seth Shostak who pointed out:

"Ray and Rob arguing shows how hard it is to find stupid life. If they can built a basic radio transmitter (and you should all ask yourself now if you can do that) then their biology doesn't matter!"

Apart from the thinly veiled implication that S.E.T.I. would not count most of the audience as 'intelligent life', Dr Shostak's point highlighted a fundamental difference between his work and that of many astrobiologists; S.E.T.I. is only interested in life-forms that can talk to us. This bypasses all the problems with defining what life is and how we should go about detecting it when it is likely to be nothing like our own (a problem previously touched on in this post).

But is it really likely that we will make contact with aliens who can communicate with us?

Seth Shostak and Ray Jayawardhana both discussed the recently launched Kepler mission which is uncovering a flood of planets, with 1235 possible candidates identified in the first year of operation alone. This is in comparison to the 500 planets that have previously been discovered in the last 15 years. This huge influx of data in such a short time indicates the vast number of planets there must be in our galaxy which suggests that it would be a miracle if we were the only life to have been created on any of them. Dr Shostak also added that S.E.T.I.'s current failure to find life should not be interpreted as an absence of extraterrestrial intelligence. Currently, S.E.T.I. has only searched a tiny patch of the sky and declaring the Universe baron of life based on such a survey would be the equivalent of searching a square kilometre of Africa and concluding there were no elephants on the continent.

On the other hand, even if life did evolve on another world, we might have a problem with timing. Robert J. Sawyer made the argument that while the human race has existed for a few thousand years, there is a much narrower window between the invention of radio (needed for communication with S.E.T.I.) and the creation of the atomic bomb. It could be that almost as soon as a life-form can communicate, it self-destructs. Dr Shostak counted this by stating that the invention of rockets would take place in the same time-frame to launch the bombs, which gave the possibility of members of the species leaving the destroyed planet behind them to colonise somewhere else. He suggested that, like cockroaches, a life-form such as humans would be impossible to fully wipe out.


So ... if you're not able to build a transmitter, S.E.T.I. consider you too stupid to be interesting. If you ARE able to build a transmitter, you are analogous to a cockroach. Everyone feeling good? Then I'll continue...


Then there is the problem that if aliens were to appear, how would we react? Contrary to popular movies, it was deemed unlikely that such a discovery would cause rioting in the streets. For one, the signal would be coming from so far away that it isn't going to affect your ability to buy your morning coffee from Tim Hortons any time soon. Secondly, 1/3 - 1/5 of the population believe aliens are here already doing (and I quote Seth Shostak) "experiments your mother would not approve of", so a significant fraction of the world would not even be surprised.

Robert J. Sawyer suggested that it might be unhealthy for our own future to discover a more advanced life-form. If it could be shown that most life did survive their 'technological adolescence', then the human race might not strive as hard to solve its own problems, being content to let time take its course. Dr Shostak took this idea to a more personal level by saying that tenured professors might find it depressing to know all their scientific research had been solved a million years ago by this advanced alien race. Professor Jayawardhana, however, seemed to think this would save on having to publish more papers!

Finally, Robert J. Sawyer pointed out that S.E.T.I. did make one very big assumption:

That life, if it's out there, would be remotely interested in us.

Moving through a living cell: a mystery

It was a suspicious case.

To all appearances, the motion within the living cell looked thermal; a movement of particles caused by heat. Yet the temperatures needed to produce that degree of motion exceeded 30,000 K. That would equal one very very dead cell.

So what was going on?

A question about living cells was a surprising one for a Physics colloquium. The visiting speaker was biophysicist Professor David Weitz from Havard University, and he assured us that he was constantly reminded by his biologist colleagues that he still thought very much like a physicist. Evidently, this had not been meant as a compliment, but it was a relief to his current audience who looked slightly fretful when cells were mentioned in the talk title.

He started off by reminding us of the random walk that particles will perform if they are suspended in a liquid. The famous experiment in which this was first observed was performed by Robert Brown in 1827 who was examining pollen grains in water. There is a rather nice demonstration of what he saw here. This effect became known as 'Brownian motion'. The cause of Brownian motion is the water molecules that are buffeting the larger pollen particles as they move around. The temperature of the water dictates how much energy the water molecules have and therefore how much they will bump around the pollen particles. Since this motion is entirely dictated by heat, it is an example of thermal motion.

There is one thing, however, that must be true for Brownian motion: the liquid must be in equilibrium and not undergoing any overall changes such as heating or cooling.

And if there is one thing known about living cells it is that they are not in equilibrium.

So how was it that when tiny beads are placed into a cell, they move in the same way as pollen grains on water?

It was strange and a closer inspection of the situation proceeded to reveal two more mysteries: Firstly, between steps in their random walk through the cell, the beads would appear trapped. They would vibrate slightly as if caught on a spring before freeing themselves to move to their next location. This small-scale movement was not seen in normal Brownian motion, so did it have a different cause or was the same force responsible on both scales?

The second oddity was that if the temperature of the cell was fixed, but all chemical activity ceased, the motion stopped. Brownian motion, being thermal, is entirely dictated by temperature. If the temperature remains constant, all Brownian-type movement should continue. Here in the cell, though, the lack of chemical activity was a clearly a key factor.

It was looking more and more as if this motion only looked thermal, but was driven by something else entirely.

Professor Weitz's group then studied the motion of the cell's microtubules. These are the most rigid structures within a cell and their movements, like that of the beads, can be measured. By creating a controlled cell-like environment in the lab, conditions within the cell could be changed to monitor their effect on the microtubules.

Really, it was a lot like simulations where I turned on physical processes such as star formation one by one to see their effects on an evolving galaxy. Galaxies ... living cells ... clearly they were all the same!

The results from these experiments pointed to the presence of a driving force that was shaking up the cell's internal network. In addition to the microtubules, the cell has a support structure of smaller filaments and it was these thinner components that were being moved about. The shaker was molecular motors; large molecules found in all living organisms. These can change their shape when they come into contact with ATP --an energy transmitting chemical-- causing material around them to deform. This motion of the smaller filaments pulls in different directions around the microtubules causing them to undergo the small-scale trapped vibrations that were seen in the beads. As the microtubules grow, they bend under this jiggling surrounding movement causing them to distort or perform a random walk, just like the pollen grains in the water.

So the cause for the microtubules or beads movement was not so different from Brownian motion in that it was the motion of the small-scale surrounding material that was having an effect. However, the reason for the background motion was not heat, but the driving force from the molecular motors.

Case closed.

On the worries of graduate students

"I worry about flying."

It was lunchtime, although we were a reduced crowd due to it being reading week at the University. No classes were held this week and, with Monday being a public holiday, many people had taken the opportunity to go away for a few days. The rest of us were looking ahead to our plans in the coming months. Graduate student Tara Parkin would be flying out to Hawaii to observe on the James Clerk Maxwell Telescope on Mauna Kea in March. She is planning to observe several relatively nearby galaxies and trace the sites of cold gas where stars are forming. Depending on the weather, Tara is hoping to collect data not just for her own research, but also for projects being investigated by two other graduate students in her research group. Starting in Toronto, the flight to Hawaii will be a long one, taking a little over twelve hours.

"There's always the possibility of health risks," Tara elaborates. "Such as blood clots in your legs."

Deep Vein Thrombosis (DVT), sometimes known as 'economy class syndrome' can occur on long haul flights due to the long periods of immobility that entails. While the risk is not high, DVT can lead to the development of a blood clot, so it is important on flights more than five hours to move a little around the cabin.

"I also worry about giving talks. Even if the people are friendly, it's sometimes worse to know you are talking to your peers!"

I had definitely felt this way before, as I mentioned in this post a few weeks ago.

"So," I clarified. "flying and giving talks are the main worries?"

"And velociraptors," interjected Max Schirm, a graduate student working with Christine Wilson. "They are not good either."

An eye to the sky

Altitude sickness, the safety liability waver form told us, was unlikely to be severe below 3000 m. At 2715 m, the location of the Gemini South telescope in the Chilean Andes should be fine for most visitors but if it wasn't, we were commanded to mention it to observatory personnel. The two hour drive down the steeply descending narrow dirt track from the mountain top was not the place to make mistakes.

When the observatory heard our plans to accompany Gemini Fellow, Dr Michelle Edwards, on a tour of the telescope, they suggested this could be counted as an official visit since many of our group were astronomers. Such listing would enable us to stay on the mountain for longer if we wished. Michelle explained that three non-astronomers were also attached to our party but it wasn't until she added that a theorist was also present did Gemini write the whole idea off and give us tourist passes.

Set on the foothills of the Andes and backing onto one of the driest deserts on Earth, Gemini's position in Chile is an ideal location for astronomers to study the southern sky. The domes of three telescopes could be seen as we ascended the mountain. The 4.1m Southern Astrophysical Research Telescope (SOAR), the Blanco 4m telescope and our destination, the 8m Gemini South.

Half-way up the mountain is a look out point with three slender metal tubes mounted on the stone wall. These resembled smaller versions of the instruments we were going to see but in fact proved to contain no magnifying lenses and were just used to guide your eye to the appropriate glittering silver hemisphere. Strangely, one was pointing at an entirely empty space which turned out to be the planned site for a new telescope, the Large Synoptic Survey Telescope (LSST).

Gemini, as its name suggests, is one of two identical telescopes both with primary mirrors that are 8m in diameter. Its twin sits on the dormant volcano, Mauna Kea, in Hawaii where it points towards the northern sky. Currently, the governments of the USA, Canada, UK, Chile, Argentina, Brazil and Australia share Gemini's operational costs to enable their astronomers to observe at the two sites.

It was swelteringly hot when we reach the mountain top, but the inside of the Gemini dome is cool. It is important, Michelle explains, to keep the inside temperature to approximately what it will be at night when the dome is rolled back to expose the telescope to the night sky. If this isn't done, the hot air rises out of the dome and over the aperture to create a phenomenon known as 'dome seeing'; the distortion of an image from turbulence due to the hot air rising. This turns the telescope's sharp view of the stars into fuzzy blobs, a waste of the excellent view the observatory has from the mountain top.

The huge mirrored dish of the telescope is supported high above us as we stand at the telescope's base. Its silvered surface is refreshed every five years by a large saucer-shaped device that is stored in the observatory's basement. The story goes that when this equipment was delivered to a port in Chile, the locals believed it to be a discovered UFO.

Climbing up the blue frame work, it was possible to peek under the mirror cover and see the surface that would, in another 8 hours, be pointed at the heavens. This giant star-studying cyclops made my eyes seem weedy by comparison.

Over to the far right was Gemini's newest tool; GeMS, a five beam laser guide star system. Stars 'twinkle' because the Earth's atmosphere is distorting the star light, an effect that is much worse for an 8m telescope than for your 1inch eyeball. To compensate for this, a system called 'adaptive optics' was developed that allows the telescope's mirror to deform depending on the atmospheric conditions to produce the best possible image. These adjustments can occur at a rate of 100s of times per minute. To measure what changes the mirror should make, most telescopes use 'guide stars'. These are stars of a known brightness that show minimal variations and can be used to calibrate the system. Gemini's new instrument goes one better than this; by firing lasers up at the sky, they can build an extremely accurate picture of how the atmosphere is distorting the light over a very wide area. While four guide stars are still needed, they can be much fainter objects and an area of the sky 2-3 times that of traditional adaptive optics systems can be 'corrected' for in a single measurement. This allows for far sharper images, especially in crowded areas of the sky --for instance near the galactic centre-- where locating a reliable, bright guide stars is difficult.

Of course, shooting light up into the sky does come with some associated risk to other, non-celestial, objects that might be in its path. If care is not taken, the laser beam could blind either an aircraft or a spy satellite.

The latter, ladies and gentlemen, is an act of war.

The average observing run tries to avoid such inconveniences by co-ordinating the times they wish to use the laser system with US space command (totally didn't make that name up). They then receive a list of times they may not use the laser system in particular directions.

Avoiding aircraft is a less sophisticated business. Although in theory, the flight paths and times of planes are known, this information is not accurate enough to be used. Instead, 'spotters' are employed to stand in regions close to the telescopes with a device like a hula hoop with which they can estimate the distance to the plane and whether the laser system will pose a risk. When an aircraft approaches, the spotters can contact the observatory and ensure the lasers are not being used.

This ... advanced ... aircraft detection technique that is apparently used by million dollar telescopes all over the world seemed so completely implausible that I demanded its verification from both Michelle and two other observers who were in our group. Their stories were consistent. I decided no observer was ever in a position to criticize an approximation I made in my simulations ever again.

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(Left image is the Gemini dome, top right is SOAR and the bottom right is the view over the mountains. Many thanks to Michelle for taking the time to proof-read this piece!)