Black Hole Hunter is an online game. This relates to a post of mine from last week about the sounds of gravity waves. If you like listening to white noise and looking at graphs then this is the game for you! If not, I’d give it a miss. I started getting a headache after a couple of minutes.
Yesterday there was brief moment when I thought that they had announced the first detection of a gravitational wave by LIGO. Needless to say, this turned out to not be the case. If it were then you would have heard about it - most likely from a newsreader doing their very best.
The paper that caused this trouble describes how LIGO has been used to place a low-limit on some properties of the Crab Nebula pulsar (you can read it here if you like). The way this paper was announced at the AAS meeting in St. Louis made it sound like they had a detection. But they didn’t and don’t (yet). Interestingly, I wasn’t all that excited though. For a few moments I was quite convinced they had finally made a detection and although it would have been historic I could only think of one thing: so what now?
The scientific community has been thinking about gravity waves for a very long time. They are a part of general relativity - although they were conceived of before that. To the non-astronomer, they basically answer the question, ‘what would happen if the Sun suddenly vanished?’. Would the Earth instantly fall out of orbit or wold it take time? Would we see it happened before or after we felt it happen?
The answer is that gravity is ‘transmitted’ via waves and that it travels at the speed of light - so we’d see and feel it at the same time. Gravity is thought to propagate through spacetime, much as light propogates through the electromagnetic field. The ripples it creates in spacetime are very tiny though and so they are extremely hard to detect.
So if you could ’see’ gravitationally energetic events, then what would you do? Well it would allow you to perform a new kind of astronomy. It would open a new spectrum of analysis and viewing on the universe. This new spectrum would range from highly energetic events (e.g. coalescing black holes) to lower energy events (e.g. accretion disks). Mainly it it interesting in the way it would let us look into the physics of black holes.
Huge amounts of money have been ploughed into gravity wave physics. Interestingly the gravity waves groups around the UK always seem to have a lot of money! They use it to meet up and discuss theoretical results. They create lavish PR campaigns and recruit PhD students. They take data with LIGO and its contemporaries. What they do not do, and have not yet ever done, is detect a single gravity wave!
I realise this is political, but it always irks me slightly. Gravity waves have lots of money but no results. ESA is potentially going to bump another project in favour of contributing to LISA, a gravitational wave detector in space.
So I am asking for anyone that knows something about gravity waves to give me some reasons to like the idea of studying them again. I used to when I was a kid. They are very cool, they are high-tech, but they are - for now - undetected and very, very expensive.
So any general relativity enthusiasts/experts out there who can offer me something to work with? Anyone?
I posted quite some time ago a response to the question ‘how does gravity work?’. It seems my answer was not satisfactory. It is still the question that I most frequently receive via email from this blog. To be fair my prior post was more specifically about how gravity changes across the face of the Earth. all the same here’s another stab at explaining what gravity is, and how it works.
I shall deal with gravity in three easy to swallow steps…
Step One: What is Gravity?
Gravity is the force felt by objects with mass, that pulls them toward other objects of mass. All mass in the universe is pulling on all other mass, all the time. You are attracting the computer screen, I am attracting the keyboard. Jupiter is pulling on your hair right now, as is the Andromeda galaxy and everyone in the room next door. Gravity is pervasive.
The strength of the pull of gravity between two masses (e.g. the mass of me and the mass of you) is determined by a famous equation, derived by Isaac Newton. In fact this equation is the subject of a t-shirt that is sold right here at Orbiting Frog.
F is the force of attraction, m(me) and m(you) are the two masses and r is the distance between the two masses. G is the gravitational constant and is a number that never changes. This kind of equation represents what is known as an inverse-square law. This refers to the fact that the force of gravity gets weaker as r gets larger by a factor of r x r. There are other inverse square laws in physics.
Step Two: How Does Gravity Work? - The Simple Answer
So having briefly covered what we’re taking about when it comes to gravity, we can now ask how gravity behaves and what is causing it. This was famously exemplified by Einstein with his General Theory of Relativity.
It is best to use an analogy here. Think of three dimensional space as a flat surface i.e. let’s ignore one dimension so our heads don’t explode. In this example we shall pretend that space is like a mattress, covering your bed.
If you put a big object on the mattress then other objects will tend to roll toward it if they get close enough. Try this yourself. Put a tennis ball on a bed and then go and put a heavy pile of books down on the bed next to it. The ball will roll toward the books, as if attracted by some force. By bending the fabric of the mattress you have created what looks like an attractive force between the two objects.
This is like the model that is used for gravity. The Sun is a very heavy object and it bends the fabric of spacetime around it, pulling objects toward it. Spacetime is the three dimensions of space plus time. You can think of it as the framework of the universe. Don’t get too carried away though, this is just a model. I don’t want you to think that spacetime actually is like a mattress! It just helps us to understand it better sometimes by making an analogy.
Step Three: How Does Gravity Work? - The Advanced Answer
So what is really happening? Why does spacetime seem like a mattress or a fabric on the face of things?
Quantum mechanics and something called the Standard Model are very good at modelling how the universe works. It tells us how three of the four forces of the universe operate. The electromagnetic force is conveyed via a particle called the photon. It is a massless piece of energy that moves through the electromagnetic field and thus transmits electromagnetic energy from one place to another. e.g. light travels from the Sun to your eyes via photons.
The strong force and the weak force are the two other forces covered by the standard model. Each of these also has a ‘carrier’ particle that transmits them across distances. These are atomic forces that only act on extremely small scales. They hold all your atoms together, so be grateful we figured them out or goodness knows what might happen!
Gravitons are postulated because of the great success of the standard model. In this framework, gravity is transmitted, or mediated, by gravitons, instead of being described in terms of our curved, mattress spacetime as above.
So why the two approaches? Well in on any large scale, the two models give the same result. The problem is that on a microscopic level, the massless graviton creates terrible mathematical issues that cannot yet be experimentally verified or corrected. Thus the graviton remains a theoretical particle… for now. Although people are looking for it.
If it exists then it fits in very neatly with the rest of physics and the graviton can start attending particle physics lunches without embarrassment. If it doesn’t fit in, then there is a problem. It would mean we have something wrong with our model and need to rethink quite a few things.
If you want to read more check out this Feynman book.
I can hardly type this without thinking of the Muppets’ ‘Pigs in Space’. Whilst writing about space debris recently, and preparing to do a talk on the subject of stuff that we’ve put into space, I got to once again thinking about those frogs that NASA put into space in 1970 (for which this very blog is named).
How many other animals have been put into space and why? Looking into the subject, it’s quite entertaining. so here’s my top ten list of animals sent into space:
10. Flies
In 1942 the first animals were put into space. they were ironically flies. Fruit flies and corn seeds took a one way trip on a US V2 rocket, (you know the ones they built using Nazi technology and slaves).
9. Dogs
On November 3rd, 1957 the first animal in orbit was Laika, the Russian space dog. She flew aboard Sputnik 2 and died during the flight. The Soviets flew 10 more dogs on that programme until April 12, 1961 when Yuri Gagarin became the first man in orbit.
Belka and Strelka (seriously, who named these dogs?) were the first mammals to be successfully returned to the Earth after orbital flight in 1960. you can them in the picture. The other canine record holders are Veterok and Ugolyok, two dogs that spent 22 days in space before returning unharmed in 1966.
Strelka’s puppy, Pushinka was given as a present to the Kennedys and many of her descendants are known still today.
8. Fish
Several fish have visited space. specifically the species Mummichog, Japanese Killfish and Zebra Danio. The Killfish were in fact the only survivors of the Columbia distaster.
More than anything I was simply pleased to find out there is an animal called a Mummichog.
7. Spiders
Experimenting with low gravity environments is obviously a big reason behind putting animals in space. So can a spider build a web in orbit? The answer is yes. Anita and Arabella were two garden spiders that flew on SkyLab in 1973.
The webs were seen to be finer that on Earth and to have variations in thickness throughout each web, unlike the highly uniform webs spun on Earth. Anit’s remains are still kept in a jar at the Smithsonian for all to see. You can see her web above.
6. Cats
Two cats have graced the skies, both put there by the French. The first was Felix in 1963, who survived his trip despite having electrodes implanted into his brain. The second cat’s name does not seem to be obvious, but he did not survive. I can has spacesuit?
5. Newts
In 1985, the Russians sent 10 newts into space after amputating their forearms. They were trying to study the regeneration of cells in low-gravity.
4. Mice and Rats
Many mice have been into space. The US reportedly put loads of them up there in the 1950s, but only the first one survived. In the 1960s, China, the USA and Russia all put many mice into space and into orbit. Nothing much seems to have come of this so far as popular culture is concerned. Douglas Adams, may have had other things to say about that though.
Russia flew rats and mice, as well as hordes of other animals, during its Bion programs in the 60s and 70s. Bion spacecraft (shown above) were designed to test organisms in space. As you can see they look very comfortable. If only NASA had made them, they would have at least had cupholders.
3. Frogs
My favourite space dwellers are the Orbiting Frogs that were sent up in 1970. Why? Well of course it was to sudy motion sickness in space. Don’t you know that frogs get carsick?
The Orbiting Frog Otolith housed the bullfrogs for a week as they circled the Earth. Scientists measured their vital signs and once the experiment was over the simply left the frogs to work it out for themselves. Needless to say it pleases and disturbs me greatly that there are possibly still two frogs up there somewhere.
Also, Toyohiro Akiyama, a Japanese journalist, carried a tree frog with him on a visit to Mir in 1990.
2. Tortoises
The tortoise is held in my esteem on this blog entry because it is the unlikely holder of not one, but two space records! In 1968 a Russian Tortoise became the first animal to go into deep space when it orbited the Moon and returned safely to the Earth.
There must be something about Tortoises that Russian space scientists like (or dislike) because a Tortoise also hold the record for longest flight time in orbit. In 1976 two tortoise and a fish spent 90.5 days in orbit on Salyut 5. They were never recovered and the craft burned up during re-entry in 1977.
1. Monkeys
Of course I had to end with monkeys. On June 11th, 1948 a monkey named Albert was the first to be put into space by NASA the Americans. He was under anesthetic during the launch and never returned. Many other monkeys have famously been put into space.
In 1959, Able and Baker, a rhesus and squirrel monkey respectively, were the first to survive spaceflight. It sounds like the premise of a Warner Brothers’ cartoon. They were placed in the nosecone of a missile and shot nearly 400 hundred miles above the surface of the Earth and over a distance of 1,700 miles. They travelled at 100,000 mph for 16 minutes. Needless to say they experience G-forces above and beyond anything normal (Wikipedia says 16g).
Able died a few days later from complications related to one of his implanted electrodes, but Baker lived until 1984 in the NASA Spaceflight centre in Huntsville, Alabama, possibly running the place.
In 1961, Ham the Chimp was launched into orbit. He was been trained to operate his craft (seriously, Warner Bros again?). He survived and lived a life of luxury afterwards. He appeared many times on television and even starred in a film with Evel Knievel!
17 more monkeys and chimps were flown in the years that followed, by the US, Russia and France, including two that went up on one of the first space shuttle missions.
I would like to end on the tragic is the story of Gordo. A young squirrel monkey from South America, Gordo also flew in the nosecone of a missile. In fact he paved the way for Able and Baker to do so more successfully a year later. He rocketed upward and survived the 10g launch, to the delight of NASA supervisors. However, during the 100,000 mph re-entry, whilst experiencing a whopping 40g, Gordo’s parachute failed to deploy. The squirrel monkey, sealed in the nosecone, sonicly-boomed into the ocean, more than a 1000 miles from Florida. He has never been recovered.
The Pioneer Anomaly is the effect seen in the paths of the Pioneer and Voyager spacecraft as they traveled out of the Solar System. An unknown force appears to be acting on them and causing them to deviate ever so slightly from their designed trajectories. This is not news, but a new study on other craft has revealed the same effect may have moved Galileo, NEAR, Rosetta, Cassini and the recent MESSENGER mission to Mercury.
Space.com has the full story and interviewed John Anderson, who performed the study. Anderson said, amongst other things, that he thought it likely that this was connected to the Pioneer Anomaly and suggested a couple of possible causes of the anomaly.
The question remains as to whether this is new physics or some problem in the way in which such objects are modelled as they move through deep space.
I did a talk on the Pioneer Anomaly last year. If you’re interested you can download the PowerPoint file here. It contains references for further reading.
A while ago I posted about the Bullet Cluster, and an image which seems to reveal the dark matter within it. Now a new image from Hubble seems to do the same thing for the galaxy cluster CL0024+17.
Now I am personally rather sceptical about the validity of images such as these, although I feel sure that we will see many more of them in the coming years. ‘Showing’ dark matter sounds to me like a dangerous business. It is, after all, dark. I would argue that releasing such images is detrimental to science and astronomy more specifically. To fool the general public into believing that something exists before you are sure of it yourself is not good science.
Now it may be beneficial to model dark matter in the way shown in these images, and this could lead to a better understanding. To release this sort of thing without warning as to the subjective nature of its content is not fair on those who would simply believe it as a photo like any other. After all how sure can anyone be that what is shown here is anything real at all? It is like deducing the nature of the wind from the way birds fly.
There is more to it that just that though. I know so many people who have no clue that many of the images they see from space are false-colour, for example. I also have to explain to people everytime I shown them Andromeda through a telescope, and look back at me confused, that the images they see from Hubble and other big observatories are enhanced, essentially doctored, to make them prettier. Do you think they will understand that this dark matter ring is simply a mathematical deduction? Will they even care?
Maybe I’m overreacting, but I do believe that one of the jobs of any scientist is to report back their findings to the public at large, who ultimately fund them. The PR guys need to get educated as to what this image and the ones that are surely coming our way soon, really mean.
Dark matter is still not a subject that we know much about. Its a mystery - and that is one very good reason it is so interesting. We cannot photograph it because we don’t know where it is. Gravitational lensing tehcniques can begin to help us locate it but don’t let’s be fooled by what the com puters give us at the end of the day. If we start to believe these images are real simply because they look real we will have strayed off the correct path and begin putting garbage into our theories. This is, as my supervisor always says, never a good thing because you end up with rubbish results; garbage in, garbage out.
You can read more over at Astronomy Picture of the Day and the Bad Astronomy Blog.
The image above shows the Bullet Cluster. Also known as 1E 0657-56, this is a pair of clusters of galaxies some 3.4 billion light years away. As Jon Davies told us in yesterday’s Astrolunch meeting however: you should be careful about believing everything you see. This image is not a regular photograph by any means. You can see the galaxies scattered about with an orange glow. This much is familiar. Layered onto this optical data is the pink, X-Ray picture from the Chandra telescope. This pink light is actually the high energy X-Ray radiation from a hot gas that permeates the cluster. Again though it is not unusual to see two different wavelength regimes seen in the same photograph.
What is unusual is that the blue ‘light’ seen here is not photographic in nature at all. It is the location of the mass in this region deduced by weak gravitational lensing - it is not a real effect but rather a mathematical interpretation of where the mass should be. As you can see it does not line up with the visual traces of the mass that we see as light and X-Ray material.
This is because it is believed that the Bullet Cluster shows us quite nicely where the dark matter can be found in this cluster. The interpretation of this image by the researchers who have studied it is that the hot, pink gas is the energy released by ordinary matter in this pair of clusters as they have collided with one another. The energy of the collision has excited the gas to emit in the X-Ray.
However not all the mass in the region is ordinary (something believed to be true about most of the universe). Dark matter is material that has mas but doesn’t interact with other, ordinary matter by the usual routes. It does not feel magnetism, or electrical forces or emit light. But is stays tethered to the ordinary matter by gravity alone.
As these two clusters collided the dark matter passed through like an ordinary pair of gaseous objects would, where as the regular, every day material became heated and disturbed and distorted in shape.
There is a wonderful video of a simulation of this hypothetical collision which you can find here.
This lovely picture adds to the already heated debate among the astrophysical community as to the existence of dark matter.
