What is a Nebula? – Updated

A nebula is a cloud of dust and gas found within the interstellar medium filling the great voids between the stars within galaxies and star clusters.

The different types of nebula consist of different elements in different proportions. Most nebulae that have not been formed by the destruction of dying stars (i.e. SNR (several types -Ia and II – will be described at a later date), planetary nebulae and those generated by Wolf-Rayet stars), contain large amounts of hydrogen gas. These nebulae if given the right conditions to compress and heat up will form the next generation of stars.

One such star forming nebula - The Eagle Nebula Credit NASA, ESA; HST

All stars, whether they are hypergiants or red dwarfs began their lives as a nebula and rather fittingly as a star dies it returns its material to the cosmos as another nebula. This nebula is either a planetary nebula or a supernova remnant, and it is through this release of matter that the universe is provided with all the elements heavier than hydrogen and helium. This includes all the material that forms the Earth and everything on it, including humans. The oxygen we breathe was formed in the hearts of red giants and the iron in our bloodstream was produced in the final days of a massive star’s existence, right before it ripped itself to pieces as a supernova. It is from this that we get the saying that we are all made of star dust, we quite literally are!

The Helix Planetary Nebula Credit NASA, ESA; HST Perhaps one day a new star will for from the ashes of the star that produced this lovely sight.

As each generation of stars further enriches the universe by spreading their life’s work as a nebula, the following generation of stars contain more of the heavier elements as there is now more available thanks to the previous generation synthesising (producing) them from hydrogen and helium over the course of their lives. Meaning that each successive stellar generation contains a larger quantity of ‘metals’ – in astrophysics a metal is any element other than hydrogen and helium – this allows different populations of stars to be identified based on their metal content. This variation is due to each successive generation of star forming nebulae contain more and more dust and metals hence creating the different detectable differences in the spectra of the stars they produce.

There are three main populations of stars though I shall keep a description of each for a further post more focused on the topic.

There are several very different types of nebulae but these types will be discussed in depth in further posts.

 

The MOST Humble Space Telescope

Space telescopes usually thought of as huge machines. The famous Hubble Space Telescope, for example, is 13.2 meters (43.5 ft) long and 4.2 meters (14 ft) in diameter. Though not all are so large; 800 kilometers above the Earth there is a satellite that is just 65 centimeters (about 25 inches) long – not larger than a large suitcase – proving that, when it comes to science, “size doesn’t matter”.

This astonishing device is called MOST (which stands for Microvariability and Oscillations of Stars). Although being very small compared to its peers, this satellite is helping scientists answer intriguing questions about stars, planets and even the Universe itself.

The MOST Space Telescope Credit: Canadian Space Agency

Staring at the Stars

Launched on June 30th 2003, MOST is the first space telescope to be entirely designed and built in Canada. As its name suggests, it is designed to take precise measurements of variations in intensity (the brightness) of stars in order to determinate their composition and age. The larger space telescopes cannot afford the time required for this task as to measure these oscillations, is necessary to keep the lens pointed at a single target in the sky for weeks at a time, and they can’t do so because of the high demand for their time.

Usually, astronomers use expensive ground-based telescopes to measure these stellar pulsations. However, this isn’t the best way to do so, since the readings are distorted by the Earth’s atmosphere. Moreover, the day-night cycle makes impossible to scientists to observe a star for 24 hours a day. Though with its orbit above the Earth’s atmosphere MOST can avoid both problems; and is able to look at any part of the sky continuously for up to seven weeks with a minimum of distortion.

The Secret life of Stars

The technology of this incredible telescope is helping astronomers figure out some very interesting things about stars, things well beyond our expectations. One of these discoveries was made as soon as the satellite became operational.

In 2004, the MOST team reported that Procyon (the brightest star in the constellation Canis Minor) shows no pulsations at all, contradicting more than 20 years of observations. Later, in 2006, the scientists realized that they were dealing with an unknown class of stars, the “slowly pulsating B supergiants”.

Furthermore, MOST has also been used to study exoplanets in alien star systems. Indeed, this is the only telescope – in space and on Earth – able to detect the light reflected by a planet orbiting around another star. Although not designed for this purpose, MOST is giving us a hint of what the atmosphere of those planets look like. It does this by detecting subtle variations in the light from either the planet or the star itself. MOST can see changes down to levels of one part to a million – or one ten thousandth of a percent!

“MOST has been very good at seeing things in the Universe that most people never expected or thought possible,” says Jaymie Matthews.

This post is part of the Young Astronomers’ Databank Project

Aurorae on Uranus

Hubble has for the first time spotted Aurorae on the distant ice giant Uranus. In the image below you can see the turquoise disk of the planet has a bright ‘blotch’.

Uranus' Aurorae Credit:NASA, ESA, and L. Lamy

An aurora is produced when a stream of charged particles from the solar wind (the material ejected from the Sun) collides with a planet’s magnetic field (more properly called its magnetosphere) and excites the particles within the atmosphere casing them to glow. This glow is what we observe as the aurora.

On Earth aurorae with a blue or red colour are due to excited nitrogen, whilst green or a redish brown hue is due to excited oxygen. The aurorae can dance across the sky in waves of coloured light and whilst some last for a few brief minutes others can remain active for hours depending on the conditions creating them – solar storms for example can create very powerful aurorae.

Aurorae have been observed on other planets as well, particularly Jupiter and Saturn; both of which have prominent auroral systems. Those present in Uranus’ atmosphere are considerably fainter and appear to last only for a few short minutes at a time.

These images represent the first observation of Uranus aurorae, with previous data collected directly during the Voyager 2 flyby in 1986.

These new observations should help to reveal more about Uranus’ magnetic field, which we currently know little about.

You can read more here

Social Science – Science140

Last week saw the launch of a new science project on twitter:

The project is hoping to collect as many science based definitions, explanations and facts all in the form of tweets which contain no more than 140 characters.

No small feat!

The project is looking for as many people to contribute as possible on all topics of science right through from Astrophysics to Zoology. Best of all anyone can take part regardless of age or experience.

What is the goal of this project you ask?

We aim to collect these definitions, explanations and biographies over the next three months in the hopes of collating them in to a book – the proceeds of which will go to charity. Details of the charity / charities will be released in the coming weeks.

Fun education from all, for all and helping out a good cause to boot, what could be better!

You can learn more about the project on the official website and on twitter by following @science140

Submitting a tweet for the project is easy, just include the hash tag – #science140

So what are you waiting for! Dust off your facts and get tweeting!

Image of the Week – Hubble’s Birthday Treat – 17/04/12

In celebration of the Hubble Space Telescope’s 22nd anniversary the ESA has released this truly stunning image of the star forming region 30 Doradus.

30 Doradus Credit: NASA, ESA, ESO, D. Lennon and E. Sabbi (ESA/STScI), J. Anderson, S. E. de Mink, R. van der Marel, T. Sohn, and N. Walborn (STScI), N. Bastian (Excellence Cluster, Munich), L. Bedin (INAF, Padua), E. Bressert (ESO), P. Crowther (Sheffield), A. de Koter (Amsterdam), C. Evans (UKATC/STFC, Edinburgh), A. Herrero (IAC, Tenerife), N. Langer (AifA, Bonn), I. Platais (JHU) and H. Sana (Amsterdam)

30 Doradus is better known as the Tarantula nebula and is located 170,000 light years away within the Milky Way’s largest satellite galaxy the Large Magellanic Cloud (LMC).

The image shows a region of space approximately 650 light years across with several million stars present within. Combined, the sum total of the stars’ masses shown in this image would be well over a million times the mass of our own Sun.

The stars are grouped into smaller clusters ranging in age from about 2 million – 25 million years old, whilst this may sound ancient in human terms as far as the universe is concerned even the oldest star in the region is a newcommer.

The brightest cluster is NGC 2070 being one of the youngest (between 2 and 3 million years old) and most actively starforming regions with the larger structure Astronomers find it an attractive region to study. Recently in fact, it was revealed that at the heart of the cluster (which contains upwards of half a million stars) there is a dense clump of stars designated RMC 136 where the largest stars yet discovered reside. Indeed several of these monsters are more than 100 times the mass of our own sun, truly cosmic giants.

The fierce output of the regions hot stars sculpts the regions gas and just into the fantastic arcs and bubbles we can see in the image. The fierce radiation bombardment of radiation is also exciting the gas and dust molecules of the nebula making them glow in their own right and classing the region as an emission nebula.

The image is composed of data from both Hubble and the ESO’s MPG/ESO 2.2-metre telescope and represents the one of the largest such mosaics in existence today. The data was captured by both telescopes during an observing run in October 2011.

You can read more here.

Introducing Miranda

To begin coverage of the Sci-Fi storyseries myself and Hannah are writing we have unveiled the first character of the story:

The ship’s AI Miranda you can read about Miranda in our new forum section here

Keep updated with more information about the story either here or on the forum!

The Young Astronomers Want … Your Sci-Fi!

This evening we bring news of a new feature here on the blog.

As well as being lovers of all things astrophysics related, myself and Hannah are massive fans of space science fiction.

We’d love to see our readers contribute their own sci-fi stories about absolutely anything, so if you’ve got any we’d love to see them and, if you’re willing, share them on the YA! All you have to do is send it to us at youngastros@gmail.com.

As part of the feature we will be publishing sections of our own sci-fi adventure story set on-board Earth’s Flagship the ESS Pisces

The story will be posted in sections when we complete them (and feel happy about showing the world!) and who knows there may be a complete version made available at some point.

We really look forward to your submissions!

See you round the Universe,

Peter & Hannah

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.

WISE Shows the Sky is Awash with Blazars

The latest release from NASA’s WISE mission has shown that just over 200 previously unidentified high energy objects are likely to be blazars.

Artist's Impression of an active Blazar Credit:NASA/JPL-Caltech

A blazar is a form of active galactic nucleus (AGN) – a galaxy where the central black hole is ‘feeding’ on large amounts of material resulting in the release of huge amounts of radiation including two tight very bright jets.

The angle at which the AGN is situated relative to the Earth determines which form of AGN we observe even though all are tied to the same processes.

In the case of a blazar we are looking directly down the AGN’s jets you could even say right down the barrel of the gun!

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

As the AGN must be lined up almost exactly with Earth for a blazar to be observed they are understandably rare compared to the other forms of AGN which have a much larger range of possible viewing angles. That being said the WISE data has the potential to reveal several thousand more.

A team using the WISE data looked at 300 objects that had previously been detected as high energy gamma-ray sources by the Fermi Space Telescope, though up to now had remained unidentified.

Using WISE the team was able to observe these gamma ray hotspots in infra-red wavelengths and showed that just over half are most likely to be blazars. WISE had also observed 50 new blazars outside those Fermi oddities along with taking observations of more than 1000 previously identified blazar candidates.

One of the project leads, Francesco Massaro has explained that there may be several thousand more as of yet unknown blazars hidden within the WISE data that could be revealed using the techniques developed for this first sample.

An image of one of the new WISE identified blazars Credit:NASA/JPL-Caltech/Kavli

You can read more here

 

NGC 2467 – Recovered

The Hubble Space telescope has given us a new insight in to the star forming region NGC 2467.

NGC 2467 Credit: NASA, ESA and Orsola De Marco (Macquarie University)

For a full size image click here

The region is a nebula composed mainly of hydrogen and it is using this hydrogen to create new stars of all masses.

Not long ago, (by astronomical terms of course!) the nebula would have been cold and dark as the newly forming stars had yet to break out of their gaseous progenitors. The most massive and thus hottest newborn stars have now blasted through the clouds of dust and gas that surrounded them, subjecting the surrounding nebula to a fierce stream of ultraviolet radiation that is eroding the larger structure and making it fluoresce in response. This fluorescence makes the nebula an emission nebula as it is emitting its own light rather than just reflecting that of the stars it contains.

Analysis of the data indicates that the majority of this radiation comes from one star. It is the bright star visible near the centre of the image.

Only the largest stars have currently emerged from their nurseries with many smaller, perhaps more sun like stars remain hidden within their denser pockets of the nebula.

NGC 2467 is like many other star forming regions including the more famous Orion Nebula. NGC 2467 is located around 13,000 light years from Earth with the Orion Nebula around 10,000 light years away.

The Nebula is located in the constellation Puppis which is completely visible to residents of the southern hemisphere (those in the northern hemisphere can observe the northern section of the constellation however it sits close to the horizon)

The image is a combination of several taken with the HST’s Wide Field Channel in several filters. The images where collected by the telescope all the way back in 2004.

Read more here