A Star’s Death Giving Life to a Monster – Recovered

3.8 billion light years away in the constellation Draco deep inside the centre of an inconspicuous galaxy, something happened at 12:57:45 on the 28^th of March 2011 that flooded the SWIFT satellite’s sensors with x-rays, and in the process sent astronomers scrambling to get a glimpse with their ground and space-based observatories.

If you look at the light curve provided by SWIFT, the x-ray brightness fluctuates considerably over a period of days. You get the first massive burst, then it calms, and then you get some more bursts days after the original event. This is very different from GRBs, such events usually consist of a huge burst of x-rays and then a dimmer afterglow of a whole variety of radiation before fading from view over a period of hours at the most. So if it isn’t a GRB, then what is it?

The massive bursts happen to be coming from the centre of the galaxy, lighting up the heart of the galaxy with the power of 1 trillion suns; outshining the galaxy itself 100 times over. Like most of the galaxy population, a super massive black hole (SMBH) happens to lurk here. Could it be that the black hole has woken up? Active galaxies emit a huge amount of radiation, including X-rays, right across the electromagnetic spectrum after all.

With data from various surveys – including FERMI and ROSAT – astronomers have concluded that before this event there has been no  sign of activity from the SMBH for the past 20 years at least, so for it to flare up without warning is very  unusual!

So far the most popular theory with the most evidence suggests a main sequence star with a mass equivalent to our sun’s wandered too close to the gravitational grip of the SMBH; a monster weighing in at 10⁷ solar masses. During a single pass it would have had to put up with one side of it being stretched and tugged at more than the other, until the gravitational pull was so powerful that the star started to get torn apart.

The matter from the disintegrated star has now settled to form a temporary accretion disk that provides fodder for the black hole. The material in the disk started to interact, and a mixture of friction and magnetic fields collimated the radiation into jets which we view as head-on, drowning out the host galaxy with its luminosity.

If this is indeed the case, the bursts of radiation seen with SWIFT and other observatories should cease after a period of months to just over a year. This would show that the star is slowly getting devoured or spat out from the accretion disk, until one day there will be no fodder for the black hole at all, and it will settle back down into its dormant state and probably won’t wake up again until the galaxy merges, or another star falls prey to its gravity well.

There is another theory I’ve picked up from Arxiv by Dokuchaev et al. which is rather more exotic:

Instead of a star being destroyed via accretion, something massively destructive happened to a star cluster near the centre of the galaxy… But first, let me focus on GRBs.

There are two types of Gamma Ray Bursts; short GRBS and long GRBs. So, what’s the difference?

Long GRBs are the most common. They’re likely to come from Type 2 supernovae, the type of supernova you get when a high mass star implodes, leaving only a core or a black hole behind. The insanely bright jets of gamma rays are thought to come from the poles of stars that are collapsing into black holes and last up to a few minutes.

Short GRBs are less common, and are likely to come from the merger of two neutron stars or a neutron star colliding with a stellar mass black hole. They last less than two seconds, but are still as destructive to anything that lies in their path as the Long GRBS.

The star cluster mentioned earlier would have a whole variety of stars to choose from, including stellar remnants such as the ones mentioned above. The stars with the most mass will migrate to the centre of the cluster, until eventually the gravitational pull of each star in the vicinity causes them to interact with each other rather destructively…

Neutron stars start to collide with each other and stellar mass black holes, creating plenty of Short GRBs as they go along. The many GRBs account for the repeating flares recorded by SWIFT and other observatories. In the period of two days 7% of the stars that make up the cluster collapsed into an accreting super massive black hole!

If this theory is correct the black hole won’t shut down any time soon like in the most popular theory, but will carry on for many years as it gains in mass over time from devouring the remainder of the star cluster and perhaps beyond.

However, I’m standing by the first theory  Either way there’s some very interesting speculation surrounding this amazing object!

You can read more on this event here and here (both in PDF format) and on NASA.

The Spiral Dance of LL Pegasi – Recovered

Hundreds of light years away in Pegasus there lies two stars locked in a gravitational dance. One star is- as far as astronomers can make out – a blue star and the other, called LL Pegasi, is a much older carbon star nearing the end of its life, and is doing so in a spectacular fashion!

Credit: ESA/NASA & R. Sahai

This is IRAS 23166+1655, it’s a beautiful sight, and one that has sparked a great amount of interest amongst astronomers recently. You can’t see the binary system itself, as it’s shrouded by the spiral of gas and dust, causing the starlight to be completely blocked. But if observed in the near-infrared you can see the two stars, revealing what is going on at the centre.

The carbon star is dying; with every pulsation another layer of the star is thrown off, creating what is known as a pre-planetary nebula; a short period in the stars life just before the final product – a planetary nebula – is created, with the temperature having risen to 30,000 Kelvin, ionizing and lighting up the gas and leaving only the core of the star behind.

With every complete orbit the star makes every 800 years or so in its gravitational dance with its companion another spiral shell is formed, with the material rushing out at 50,000 km per hour!

The ionization has yet to take place to create the final planetary nebula, so how is it that you can see the pre-planetary nebula at all? If you look carefully at the spiral you’ll notice the right side is more lit up than the other, this side of the spiral happens to be the nearest to the galactic plane where the highest concentration of stars is and therefore the highest concentration of starlight. The nebula is lit up by the starlight!

The paper written on LL Pegasi by M. Morris et al has a diagram showing where the galactic plane lies in relation to the nebula, so do have a look! It’s also a very interesting paper to read 

You can read more here, and the paper is here (in PDF format)!

Quasars and 3C273 – Recovered

3C273 Credit: SDSS

The central object looks just like any other star in the image above, but it’s as far from a star as you can get. It is in fact a Quasar (the less catchy name is Quasi-Stellar Radio Source), which are some of the most distant and most luminous objects seen in the observable universe. This one however isn’t as distant as many of its type, at just a redshift (Z) of 0.15 it’s just 1.88 billion (yes, just) light years away [1].

Some of the most distant Quasars have a Z of 6, placing them around 12 billion light years away, or 24 billion light years away in commoving distance. One such example is SDSS J1148+5251 which has a Z of 6.41. It was until recently the most distant quasar found, but this record has been replaced by CFHQS J232908-030158 at a Z of 6.43, placing it 12.8 billion light years away [2].

Most of these objects appear as point-like objects, which is why they look exactly like stars in images. Most galaxies at high redshift are hard to see, so why are Quasars so luminous that they can be seen at such great distances; and what are they anyway?

Quasars are a type of Active Galactic Nuclei (AGN). If you could see in detail the nucleus of any galaxy that is classified as ‘active’ you’ll see a doughnut shaped torus of matter surrounding a more compact, thinner accretion disk which in turn surrounds the galaxy’s super massive black hole.  And all this could fit snugly inside a solar system!

The black hole at the centre of this powers the AGN. The huge gravitational pull from the black hole drags matter into its vicinity, surrounding itself with an accretion disk in the process. As the matter travels round the disk, it releases energy due to the friction caused by the material in the disk interacting with each other as it races round at thousands of kilometres per hour. The radiation emitted ranges from gamma rays to radio waves, and the sheer amount of radiation emitted can cause an AGN to completely outshine its host galaxy by hundreds of times!

The powerful magnetic fields caused by the AGN can also cause material to collimate into jets of plasma. This plasma races out of the galactic nucleus along the black hole’s spin axis at relativistic speeds, stretching out for thousands upon thousands of light years. The creation of these jets is still under a lot of debate, but currently it is thought that the material in the accretion disk escapes via the hole in the disk – which compared to the rest of the disk, is relatively dust free. The material escapes in this direction simply because there’s less resistance.

There are different types of AGN, from radio galaxies to Blazars.  The AGN are basically the same thing, just viewed at different angles:

AGN at various angles; Credit: Aurore Simonnet, SSU NASA E/PO.

A Seyfert 1 for instance is where the AGN is viewed at a 30 degree angle and a Seyfert 2/ Radio galaxy is viewed at a 90 degree angle and so on. A Quasar is viewed at a 30 degree angle, so is it not just a Seyfert galaxy? What differentiates a Quasar from a Seyfert is the luminosity; an AGN with a luminosity of over 10¹¹ L_?is classed as a Quasar [3].

Back to the Quasars and 3C 273…

3C273 was the first Quasar to be indentified in 1963, when Maarten Schmidt published a paper in Nature, after the star-like object was associated with a radio source already documented in the Third Cambridge Catalogue of Radio Source [4]. Schmidt’s paper showed that 3C273 has a high redshift, placing it billions of light years outside our own galaxy.

This particular Quasar has a jet that stretches out for 60 kilo parsecs in length, making it almost twice the diameter of our galaxy [5]! You can see the jet in figure one; it’s the faint streak just below the quasar on the bottom right. This jet makes 3C273 one of just 10% of Quasars that have large scale jets as big as 3C273’s [6]. The other 90% have less powerful jets that are just parsecs in length.

Quasars aren’t seen (to the best of our knowledge) after a redshift of 0.06; they become more common the higher the redshift. Why are there more Quasars in the early universe? The universe was full with young galaxies absolutely brimming with new stars and therefore plenty of gas for a super massive black hole to consume. Eventually the fuel runs out, either by the AGN exceeding the Eddington luminosity, where the AGN becomes so bright the photons it emits buffets the gas out of the way and prevents it from falling in, or simply by the AGN having consumed all the available material.

List of references:

[1] SDSS DR7 ObjID: 587726014535237707

[2] Willot C. J et al (2007) “Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey” Astro-ph:arXiv:0706.0914v2.

[3] Sparke, L.S. and Gallagher, J.S.  (2000) ‘’Galaxies in the Universe: An Introduction’’ 2nd ed.  New York: Cambridge University Press.

[4]Schmidt. M. (1963) “3C273: A Star-Like Object with Large Red-Shift”. Nature 197: 1040–1040. doi:10.1038/1971040a0.

[5] Uchiyama. Y. et al (2006) “Shedding New Light on the 3C 273 Jet with the Spitzer Space Telescope” Astrophys. J. 648 910 doi: 10.1086/505964

[6] “UT Austin scientists find evidence that all radio-loud quasars may be blazars’’. The University of Texas (14/2001)http://www.utexas.edu/news/2001/06/14/nr_blazers/

The Young Astronomers Need You!

The Young Astronomers are expanding! We’re currently developing a website full of new features and content, with an accompanying blog that will be host to all the latest articles by our editors and guest bloggers. For now though we’re lurking on Sigma Orionis, as our original blog is sadly beyond repair despite weeks of attempts to get it back in operation.

At the Young Astronomers we have big plans ahead of us, but more immediately we need more editors (or guest bloggers; if you don’t want to be committed then just doing the odd article with us is fine) so we can provide more content covering a wider range of topics – at different levels of interest – concerning everything possible to do with astronomy and space (except astrology )

To apply all you need to do is write a post on whatever space-related topic you’d like and send it to this email address – youngastros@gmail.com, and we’ll get back to you as soon as we can.

We’d also very much appreciate podcasters, so if anyone would like to do a podcast for the site it would be most welcome as unfortunately the two resident podcasters – Hannah and Peter – don’t have as much time on their hands as they would like to keep up a regular one.

We’re very eager to recruit more people into the YA to make it into what we imagine it to be; a hub of young astronomers (and of cours people of any ages), so we hope you can join us!

What do Astronomers do: Professor Bill Keel – Recovered

Professor Keel Credit: Jeff Hanson

Bill Keel is a professor of physics and astronomy at the University of Alabama and is also part of the team at Galaxy Zoo. He is the author of The Road to Galaxy Formation and The Sky at Einstein’s Feet ( a book that I thoroughly enjoy  ). Bill kindly let me interview him about what he does as an Astronomer, my questions are in bold.

How did you become an astronomer?

My family thinks it has to do with my grandfather continually pointing out the Moon as we sat on a porch swing. Beyond that, in the 1960s space was big news all the time, and new things were happening constantly. By the time I was about 14, astronomy had seized my brain. I mowed yards for a summer to buy a secondhand 6-inch telescope, whose bright and crisp views were a revelation to me. Then it was off to college and I’ve never looked back on the choice.

What are your areas of research?

Galaxies – anything involving galaxies, it seems I can’t get enough of. Active galactic nuclei, galaxy interactions, galaxy evolution, dust in galaxies, I dabble in the whole range.

How did you get involved with Galaxy Zoo and what do you do there?

I saw a notice (I think it was on the BAUT forum) and found the Zoo forum. Within a few days, I was seeing lots of interesting galaxies that Zooites were posting for discussion and couldn’t help noticing the research uses of some samples of these. So I asked for people to watch for overlapping galaxies and the rest is history. The next year I found myself part of the GZ team. As it’s worked out, I get involved in a lot of science generated by things posted on the Forum, rather than just the initial Zoo goals. This is also a great audience for education and public outreach, so I do posts answering various questions or explaining bits of astronomy. I recently realized that all of my current research grants involve projects spun off from the GZ forum!

What does observing with ground-based and space observatories involve?

Ground-based observing can be a very intense experience, since you may only have a few nights allocated to do a project. During that time, you need to make sure the instrument is performing to specifications, get a check all the necessary calibrations, and make (the mythical) optimum use of the time and conditions. On top of that, and helping make it worthwhile, is that some of us find observing, even with computers intervening in so many ways, to foster a strong sense of connection with the Universe (Sandy Faber also described this, possibly in the oldish “The Astronomers” TV series). These days, the better description of the process would be “taking data, where the goal is to get certain measurements of required quality (and those measurements may be fairly complicated derivatives of your original data). Every night at the telescope (or hour, if you’re a radio observer) may require many times that long in data processing. Scripts can be your friends. Working from the ground, it sometimes helps to take a philosophical view – weather may wipe you out unexpectedly no matter how long you’ve waited for an observing session. (For example, unexpected high winds have brought a stripe of clouds over Kitt Peak, which I’m looking at with disapproval). As my gradate adviser pointed out, it’s easier to be philosophical and wait for another night when you already have a permanent job!

For space facilities, things are of course hands-off. Typically, one proposes a project, which gets reviewed by a committee trying to figure out which 15% of proposals to accept that will actually fit in a given year’s calendar. Then you prepare a detailed description of the observations, and send it in. For all but a few special cases, the next you hear is when the observations are scheduled and your data are being processed to send to you. It’s a different way of working, and to make best use of these facilities you need working knowledge of some facets of orbital dynamics and the space environment (plus a large pile of PDF documents that the agencies think you should be familiar with – my favorite was the 120-page document on changes to Hubble operations with only two gyros that proposers were supposed to have read in its entirety.)

Learn more about Bill Keel at his personal website:http://www.astr.ua.edu/keel/ or follow him on twitter at:@NGC3314

What Happens when the Average Banana Travels at Close to the Speed of Light?

This is the first in a series of blog posts concerning the mathematical side of physics and astronomy!

So what does happen when the average banana travels at close to the speed of light?

Attempt Number One:

Credit: legoalbert

Take two average sized bananas of 8 inches (0.2032 metres) in length with an average weight of 120g (or 0.12kg) and place one of them in a space ship that has a nice shiny warp drive and leave the other banana back on Earth. Launch said awesome spaceship (oh, and make sure both bananas have an atomic clock with them) and set it to a velocity of 99.9% the speed of light (or 2.995×10^8 m/s). Finally, observe the bananas from Earth and measure to your pleasure.

Oh hang on, we can’t do that, but wait…

Attempt Number Two!

We now resort to doing this theoretically, which admittedly isn’t as fun as doing it all with a spaceship but still. Using the equations below we can see what will happen to the banana (and spaceship).

We begin with two bananas, with one in a fruit bowl on Earth and the other about to leave our planet’s orbit at 99.9% the speed of light. The banana in your fruit bowl is at rest relative to the space banana, so there is no noticeable effect on time whatsoever. However, time acts very oddly for our space banana as we will find out using this equation:

Where t₀ is the time passing for the banana back on earth according to its atomic clock, t  is the time for the banana in space according to the spaceship’s clock and  (gamma) is the Lorentz Factor. The Lorentz Factor is just a shorter and fancier way of saying:

Where v  is the velocity of the space banana and c is the speed of light in a vacuum.

So, with every second that passes for the space banana, 22.65 more seconds pass for the fruit bowl banana. However the space banana’s perception of time would be exactly the same as ours, but once its craft has returned and we saw its clock it would show that time had indeed been passing far more slowly at high velocity than it would have on Earth.

Now for the lorentz contractions…

Not only would the banana’s time get skewered by the high velocity but its length would too as shown in this equation:

Where l  is the length of the banana as perceived by an observer back on earth and l₀ is the length of the earth banana at rest.

Using the equation above you can see that the average banana of 8 inches in length will contract down to just 0.36 inches if it’s travelling at 99.9% the speed of light! If the ship itself is, say, 4 kilometres in length, it will contract to 1.66 km.

This is of course to the observer’s perspective.  Someone aboard the ship would perceive the length of the craft, the banana and themselves to be the same length they would be if they were at rest.

Length and time isn’t the only thing that goes weird at these speeds, mass also goes haywire! Here’s what you use to calculate the mass of the banana:

Where m is the mass of the banana at high velocity, and m₀ is the mass of the banana at rest. So, the rest mass of our banana is 120 g but once it’s at 99.9% c its mass increases to 3.45 kg!

Peter and I will soon go into more detail about how and why these phenomena exist in a series of blogposts on General and Special relativity!

The Mobius Strip in the Galactic Centre

ESA/ NASA/ JPL-Caltech/ Hi-GAL

Well, to our 2D point of view at least. If you look at it overhead it’s actually a ring that’s bent in the middle. But I digress…

Heading down towards the centre of the Milky Way you start to find you’re completely shrouded in molecular clouds of various densities and sizes. Head down deeper into the galactic centre and you’re in the home of the largest and densest molecular clouds of the lot; the home of copious amounts of star formation.

It’s also where the object of S. Molinari et al’s attention lies: A distorted ring 30,000 light years away from us that was recently the attention of the Hershel space telescope. The ring is ~326 light years in diameter and weighs in at 3 x 10^7 . It’s composed of cold (and when I mean cold I mean just 15 degrees above absolute zero!) gas and dust, and completes an entire orbit around the galactic centre once every 6 million years according to the model provided in S Molinari et al’s paper.

The authors of the paper also cautiously suggest that it could be the remnant of the accretion disk our galaxy had when its central black hole was active; something that is thought to be part of the evolution of a galaxy such as ours.

It has also been suggested that its structure could be due to interactions with the Andromeda galaxy, which could explain the rest of the vicinities structure.

Here is a link to the paper: A 100-parsec elliptical and twisted ring of cold and dense molecular clouds revealed by Herschel around the Galactic Center

And the press release.

The Young Astronomers

As you may have noticed The Young Astronomers website redirects to here. The Young Astronomers – which we both help run – is currently down due to server and plug-in problems which caused various annoyances while browsing and locked the admins and editors out of the admin section. All new YA content is being posted here until the site’s back up and running, and any posts will then be transferred later.