In the show this time, we talk to Dr Jeronimo Bernard-Salas about circumstellar and interstellar fullerenes, Stuart rounds up the latest news and we hear what we can see in the March night sky from Ian Morison and John Field.
This month in the news: a star's final flarewell, black hole records and a new notch in the Van Allen belts.
As the largest stars start to approach the ends of their lives they will run out of hydrogen in their cores required for nuclear fusion, this results in a drop in the amount of energy which pushing on the stars outer layers. The star is then constricted as gravity pulls the star in on itself which acts to heat up the core and allow the fusion of heavier elements to begin resulting in a new outflow of energy which stalls the the collapsing effects of gravity. However, once a star begins to fuse elements as heavy as iron the amount of energy given out is less than what must be put in. This results in a solid core within the star which contributes nothing to fight against gravity and itself is held up not from fusion processes but the degeneracy pressure which arises between tightly packed electrons. When this happens the star is in its final death throes, the outer layers are no longer supported and begin to rapidly fall onto the core which itself grows in mass until the electron pressure supporting it fails and the core collapses. At this point, the core will become a sphere of tightly bound neutrons that is so dense that the in-falling outer layers of the star bounce back. This causes a shockwave which drives back through the entire remainder of the star and for a short time produces such tremendous amounts of energy that the explosion will outshine all the light from all the other stars in its host galaxy. This is known as a core collapse supernova.
Though the story of the end of a stars life is generally understood, we are still missing the critical information about how a star is behaving just before going supernova. The reason for this is part theory, in that we do not exactly know how changes within the core of the star will manifest themselves on the surface, and the other is observational, because we have never actually observed a star just before it goes supernova. Fortunately the latter problem has been partially resolved with recent work from an international group of scientists who happened to observe a star just over a month before it went supernova in 2010. The team observed the progenitor star undergoing a huge mass ejection from its surface, a super solar flare, which contained as much material as six Jupiters. A violent outburst such as this is predicted by the wave-driven outburst model, which says that for some stars, as they begin the process of fusing elements heavier then carbon, will have a short period where it produces an excess of energy. This drives both irregular convective currents and a series of powerful waves through the star which results in a large amount of material unbinding itself from the stars surface in all directions.
The team hope that the observations of the supernova SN 2010mc and its progenitor star will help provide that causal link between what is happening to a star before it goes supernova up to the point when it finally explodes. Of course this is just a single observation of one particular type of star and there is no way of knowing just yet whether or not the other theories for what should happen before a supernova occurs are more prominent throughout the universe.
The galaxy NGC 1365 contains in its centre one of the powerful phenomenon in the Universe, an active galactic nucleus or AGN. The AGN in NGC 1365 is the result of its 2 million solar mass black hole gorging on the plentiful supplies of gas and dust that surrounds it, forming a bright luminous disk of in falling material and a huge jet spewing any left overs into intergalactic space. What makes the study of AGN important is that they are a way of studying the supermassive black holes within galaxies and it is from these supermassive black holes we think the seeds of the first galaxies formed. In this way supermassive black holes can be thought of as the fossil record of a galaxy as the black holes properties relate to all the major past events through which its host galaxy underwent. One interesting property of these black holes which astronomers have been wanting to study is their rate of spin. A black hole which is spinning slowly tells us that during its early formation it fed upon the slowly moving gas and dust which was within its immediate surroundings but a black hole that spins rapidly indicates that at some point in the past dramatic events such galaxies colliding must have occurred.
Observing the rate at which a black hole spins requires detecting the x-rays being emitted by the material close to the black hole's event horizon. The XMM-Newton satellite had measured the low energy x-rays being emitted from the supermassive black hole in NGC 1365 in the past and deduced that the black hole could be spinning extremely fast, almost as fast as Einstein's theory of relativity would allow. However the result was contentious as some astronomers pointed out that the thick layers of dust which surround the black hole could be distorting the x-rays in a way similar to what may be expected from a spinning black hole. Fortunately though a second follow up experiment, NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) satellite, made measurements of the high energy x-ray emissions. By combining both the data from XMM-Newton and NuSTAR astronomers were then able to confirm that in fact the supermassive black hole in NGC 1365 is rotating rapidly and that at some point in the galaxies distant past it must have collided with another galaxy.
And finally about 55 years ago James Van Allen discovered two regions of charged particles that wrapped around the Earth from pole to pole a few thousand kilometers above the surface. The two regions were named in honour of their discoverer, the Van Allen belts. The two belts are formed when charged particles, such as protons and electrons, are spewed out of the Sun as solar winds become trapped within folds of the Earth's magnetic field. Although considered a well understood phenomena it is important that the belts can be modelled accurately as the outer belt made up of electrons can expand and shrink on timescales of less than a few days being very sensitive to the effects of the changing solar wind. The inner belt made up of protons can change too but changes on much longer timescales of years to decades. Understanding how the belts may change is important because they may pose a danger to communication and GPS satellites which are critical to modern life.
When NASA launched the two Van Allen Probes to study the belts late in 2012 it was expected that no major new science would be found but instead just an increased understanding of how the Van Allen belts behave. However for one month from September 2nd 2012 they observed the formation of an entirely new belt of high-energy electrons which coincided with a major shockwave in the interplanetary magnetic field caused by a sudden spike in solar activity. What surprised astronomers most though, was that the new belt remained remarkably stable until its disappearance in early October yet at the same time it was responding immediately to any changes in the solar wind.
These observations of the Van Allen belts have brought about a new understanding of how the Earth's magnetic field interacts with the Sun and its surrounding environment that was completely unpredicted by theoretical models. It is at these moments when observation leads theory that the most exciting new science can occur and is a good lesson in why you should never take even the most understood phenomena in the Universe for granted.
Interview with Dr Jeronimo Bernard-Salas
Dr Jeronimo Bernard-Salas talks to us about observations of circumstellar and interstellar fullerenes. These carbon molecules have been observed in a lot of different environments, from star-forming regions to very old and evolved stars. In this interview, Dr Bernard-Salas explains the different mechanisms for their formation and evolution in these environments.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during March 2013.
The constellations of Orion, Taurus, Gemini and Auriga are gradually moving out of view towards the west. Leo lies to the west of Gemini, with a fairly empty part of the sky in between containing Cancer. The open star cluster M44, the Beehive, is at Cancer's heart, and is lovely in binoculars. Procyon, the brightest star in Canis Minor, is below it. The Sickle of Leo forms the Lion's paws and includes the bright star Regulus. Beneath his belly are a number of galaxies which can be seen using binoculars or a small telescope. M105, M96 and M95 form a trio, with M66 and M65 further over. Between the stars Denebola - in the Lion's tail - and Arcturus in the constellation of Boötes, is Coma Berenices and the northern part of Virgo. This apparently sparse region of the heavens is known as the Realm of the Galaxies, and looks towards the giant Virgo Cluster of galaxies. Binoculars or a small telescope pick out a number of Messier objects there on a dark night. Ursa Major, the Great Bear, is above Leo and contains the asterism of the Plough, otherwise known as the Big Dipper. The middle star of the handle of the Plough is a double star, Alcor and Mizar, that can be separated with the naked eye. A small telescope shows that the brighter star, Mizar, is itself a double, and there is another, reddish, star in the same field of view.
- Jupiter is moving through Taurus and appears slightly further west each night, along with the rest of the southern sky. It is moving eastwards relative to the stars, however, and is about 5° from the star Aldebaran. Its angular diameter decreases from 39 to 36" during the month, but surface detail and the Galilean moons are still visible through a telescope.
- Saturn only rises 25° above the horizon, but is becoming more visible in the evenings. It rises around 23:30 UT (Universal Time) at the beginning of the month, reaching its highest point in the south at 04:30. By month's end, it rises at about 21:40 and crosses the south at 02:00. Its magnitude brightens from +0.4 to +0.3 during March, and it grows from 18 to 18.6" in angular size as the Earth approaches it. Its rings are now at angle of around 19° to our line of sight and hide much of the planet's northern hemisphere. You may spot Cassini's Division between the rings with a small telescope.
- Mercury reaches greatest western elongation (furthest point from the Sun in the sky) on the 31st, and is low in the east-south-east at dawn. It may be spotted through binoculars, but don't use them after the Sun has risen.
- Mars is in Aquarius, and appears just 3° above the south-western horizon at sunset at the start of the month, before becoming lost in the Sun's glare as March progresses. Binoculars are probably required to see it, but wait until the Sun has set before using them. Mars will be just 39" from Uranus on the 22nd, the planets at respective magnitudes of +1.2 and +6. You will only be able to spot them with a telescope and a very low western horizon, however.
- Venus reaches superior conjunction (behind the Sun in the sky) on the 28th and is therefore not visible this month.
- Comet PANSTARRS should be visible from the 9th to the 20th. It reaches perihelion on the 10th and is then closer to the Sun than is Mercury. It will probably be at its brightest from the 12th to the 17th for observers in the UK, appearing low in the west-north-west. It is just above a thin crescent Moon on the 12th, and will appear close to the Andromeda Galaxy on the 4th of April.
John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during March 2013.
Early in the month, Comets Lemmon and PANSTARRS should be visible in the south-west after sunset as the nights lengthen. The summer constellations of Taurus, Orion and Gemini can be found in the north-east in the evening, but move towards the western horizon during the month. The Pleiades Cluster is in the north-west a little later in the evening. To Māori, it is Matariki - the Little Eyes - and is important in the annual calendar. Binoculars or a telescope reveal many stars. The V-shaped head of Taurus the Bull follows the Pleiades, with the planet Jupiter between them. Jupiter is growing fainter as it moves away from the Earth. The brightest star in Taurus is the orange-coloured Aldebaran - the Follower in Arabic - which marks one of the Bull's eyes. The Hyades Cluster forms the fainter part of the Bull's head, and contains the half-sisters of the Pleiades according to Greek mythology. The cluster hosts a number of multiple stars among more than 100 that are brighter than magnitude +9. The zodiacal constellation of Cancer the Crab appears in the north as four stars with a haze at the centre. This haze covers an area some three times greater than that of the full Moon, and binoculars show it to be the Beehive Cluster. Leo the Lion rises at sunset and follows the Crab across the sky. First associated with Persian culture, to the Ancient Greeks this became the lion slain by Hercules for the first of his twelve tasks. Regulus, the brightest star in Leo at magnitude +1.4, is a blue-white star with a red companion of magnitude +7.6 that can be seen through binoculars or a small telescope. The planet Saturn rises in the east before midnight, in the constellation of Libra.
The Milky Way runs from north to south in the evening, and is brightest near the southern horizon. It is Te Ikaroa - the Long Fish - to Māori in Aotearoa (New Zealand). This is the path along which Tama-rereti sailed across the sky as he placed the stars into the heavens. Its mottled appearance comes from clouds of interstellar material that block the light of the more distant stars. The constellation of Crux, or the Southern Cross, sits in the southern part of the Milky Way along with its pointer stars. The different parts of the great ship Argo lie between Crux and Canis Major. The largest constellation until 1752, it is now divided into Carina (keel), Vela (sails) and Puppis (poop deck). Carina is full of naked-eye objects, including Canopus, the second-brightest night-time star at magnitude -0.72. According to Greek legend, Argo carried Jason and his crew in their quest to find the Golden Fleece, and it sails along the Milky Way with its keel pointing towards the south celestial pole about which the sky appears to rotate. The Clouds of Magellan are near to the star Achernar in the south, and can easily be spotted with the unaided eye on a dark, moonless night. The Clouds are, in fact, two small galaxies approximately 200,000 light-years away.
The autumnal equinox arrives on the 20th, when the day and night will be of almost equal length and the Sun will rise due east and set due west. The planet Mercury appears in the morning twilight this month, making its best appearance of the year and rising due east at dawn by the middle of the month. An orange-looking star to the naked eye, it resembles a tiny crescent Moon when viewed through a small telescope. Venus and Mars, meanwhile, are almost behind the Sun from our perspective and are therefore hidden.
Odds and Ends
On the 25th February 2013, a small satellite, Strand-1 (Surrey Training, Research and Nanosatellite Demonstrator), was launched into space. This satellite contains a smartphone which will eventually control parts of the satellite as well as running apps such as "Scream in Space". This satellite also tests two new propulsion systems: Pulsed Plasma Thrusters and the WARP DRiVE (Water-Alcohol Resistojet Propulsion Deorbit Re-entry Velocity Experiment).
Precision planet-hunting: the smallest exoplanet yet has been discovered with the Kepler space telescope. The planet was one of three discovered orbiting the star Kepler 37, and is estimated to be smaller than Mercury but slightly larger than the Moon. The planet, Kepler 37b, orbits its parent star about at about a third of the Mercury-Sun distance.
A vote has been held to find names for the fourth and fifth moons of Pluto. The winning names were Vulcan and Cerberus. These will be out forward to the International Astronomy Union who will ultimately decide the new names.
|Interview:||Dr Jeronimo Bernard-Salas and Liz Guzman|
|Night sky:||Ian Morison and John Field|
|Presenters:||Indy Leclercq, Christina Smith and Chris Wallis|
|Editors:||Christina Smith, Claire Bretherton, Liz Guzman and Mark Purver.|
|Segment Voice:||Mike Peel|
|Website:||Christina Smith and Stuart Lowe|
|Cover art:||A true-colour image of the major part of NGC 1365, combined from three exposures with the FORS1 multi-mode instrument at VLT UT1, in the B (blue), V (green) and R (red) optical bands. CREDIT: ESO|
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