In the show this time, we talk to Dr. Debora Sijacki about cosmological simulations, Indy rounds up the latest news, and we find out what we can see in the June night sky from Ian Morison and Claire Bretherton.
In the news this month: the origin of jets, another Kuiper Belt and the future of telescopes on Mauna Kea
Active Galactic Nuclei are some of the brightest objects in the universe, emitting large amounts of radiation across the electromagnetic spectrum. As such, they are an extremely interesting category of objects for astronomers to observe - especially in the radio band, where a number of AGN and their host galaxies exhibit phenomena known as jets and lobes. The emission from these radio galaxies is due to a process called synchrotron radiation, whereby free electrons are accelerated to relativistic speeds by magnetic fields, and emit light at radio wavelengths. The result is usually quite spectacular, showing astronomers a pair of very large 'lobes' of extremely hot gas or even plasma, coming away from the nucleus of the galaxy in symmetrical fashion. These are suspected to be generated by very compact and energetic 'jets', also made up of plasma which are somehow beamed out of the galactic nucleus, and which link the nucleus and the lobes. These are sometimes visible in active radio galaxies. Despite their brightness, comparatively little is known so far about these radio-loud AGN and their interesting jets and lobes. They are predominantly found in elliptical galaxies, although there is no single explanation for this (many complementary theories have been put forward though, such as more massive black holes being found in ellipticals, or a richer intergalactic medium).
Another mystery was why some AGN possessed visible jets and lobes, and others did not. This appears to have been solved recently by a team of astronomers using the Hubble telescope's Wide Field Camera 3 to study a population of known radio galaxies. As they were investigating the images, they realised that all the galaxies they were looking at were the product of mergers - that is to say, the collision of two galaxies to form one. When this happens, the black holes at the center of the two parent galaxies end up rotating around each other at extremely high energies, to finally merge. This huge burst of power appears to be what powers the extremely energetic jets. The work was done by Marco Chiaberge and colleagues at the Space Telescope Science Institute. They studied a sample of 19 radio galaxies and found that all of them had irregular shapes, and regions of intense star formation – telltale signs of a recent merger. Some mergers don't produce jets, but this could be due to the fact that the black holes involved in the process are still falling towards each other and haven't actually merged yet. In the case that they do come together, the final, larger black hole would be spinning faster and have a stronger magnetic field, thus ejecting charged particles to its surrounding disk of gas at extremely high speeds, and powering the spectacular outflows that radio astronomers see. While the precise mechanism of the jets and lobes is still not known, this discovery lends credence to the theory that the black holes are behind it all.
In other news, Astronomers have discovered debris around a nearby star that looks a lot like the Kuiper belt. The Kuiper belt is the region of our solar system beginning just after Neptune and extending to 50 AU away from the Sun. It is home to a host of small asteroids and bodies made up of ices (water ice, methane ice and ammonia ice) and three dwarf planets: Pluto, Haumea and Makemake. Astronomers suspect that most of the material in the Kuiper belt is lefto over from the formation of the icy planets in our solar system. A team of scientists using the Gemini Planet Imager, an instrument on the Gemini South telescope in Chile, have discovered a ring of material extremely similar to the Kuiper belt around a nearby star that is just 15 million years old - a mere baby in astronomical terms.
The star is only about 360 light years from our Solar System, and the ring of debris surrounding it is located at about the same distance the Kuiper belt is from our Sun, and recieves roughly the same amount of light. This is an extremely important find, as it could enable astronomers to study a system very similar to our own solar system in its infancy. They have also found that the center of the ring is offset from the star, which could suggest the presence of an unseen exoplanet as large as Jupiter. Observations of the system will continue, and another instrument similar to the GPI called SPHERE is also looking for such systems. With more discoveries surely to come, the history of our solar system will slowly begin to reveal its secrets.
Finally, construction of the thirty metre telescope, or TMT, on the Hawaiian mountain Mauna Kea, is going to go ahead as planned - but the rules and regulations governing astronomical facilities located on the mountai are going to undergo significant change. Mauna Kea is seen as a sacred space by the Hawaiian people, and the many telescopes that have been built on the mountain are seen by some as violations of an important cultural site. Protests broke out in April after construction began on the TMT, despite the project having gone through a long permissions process to be able to go forward. The land TMT and other telescopes are built on is leased from the Hawaiian government as a Science reserve, by the University of Hawaii. The TMT construction is set to resume, but on the condition that 25% of the other telescopes would cease operations and shut down by the time TMT is ready. It remains unclear how the telescopes will proceed, and a number of legal challenges are being fought in the Hawaiian courts. This issue highlights the ethical and cultural issues that astronomers can face when looking for appropriate telescope sites, and whatever transpires will be of interest to the broader astronomical community.
Interview with Dr. Debora Sijacki
Dr. Debora Sijacki from the University of Cambridge is a cosmologist who specialises in developing large-scale simulations of our universe. She describes the basic principles behind building simulations of very large chunks of the universe, and explains what we can learn about various astrophysical phenomena from these simulations. Dr. Sijacki also talks about the limitations of numerical models, and what the future holds for an ever more useful tool used to explore cosmology.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during June 2015.
The constellation of Leo the Lion is setting in the west after sunset, with the asterism of the Sickle forming its mane and Regulus as its brightest star. The planets Jupiter and Venus are both found here later in the month. Towards the South is the Realm of the Galaxies, in Virgo and Coma Berenices, where a telescope can pick out many deep-sky objects. The bright star Arcturus, in Boötes, resides nearby. Cygnus the Swan and Lyra the Lyre are rising in the east, with Hercules in between them and Boötes. The Summer Triangle, composed of the stars Altair in Aquila, Deneb in Cygnus and Vega in Lyra, is visible. One third of the way from Altair to Vega lies the Cygnus Rift, a dark region of dust in the Milky Way, which hosts Brocchi's Cluster, also known as the Coathanger. Ursa Major is almost overhead.
- Jupiter is still bright in the south-west at nightfall. Its brightness declines from magnitude -1.9 to -1.8 during the month, while its angular size drops from 35 to 32.5". It moves from Cancer into Leo on the 9th and heads towards Regulus. Although the current apparition is past its best, a small telescope can still show Jupiter's equatorial bands and its four Galilean moons.
- Saturn reached opposition on the 22nd of May, so it is visible in the south-east after dark and crosses the southern sky during the night. It is moving retrograde (westwards) through the eastern part of Libra, close to the fan of three stars marking the head of Scorpius the Scorpion and only 3° from the double star Beta Scorpii. The planet is 18" across, and the rings span 41", tilting at 24° to the line of sight. However, Saturn's low elevation, never rising above 20° from the UK, makes atmospheric blurring a problem when observing it closely.
- Mercury was at inferior conjunction (between the Earth and Sun) on the 30th of May, so it is not visible for the first part of June. It then climbs slowly into the pre-dawn sky, reaching western elongation (its greatest separation from the Sun in our sky) on the 24th. It has a magnitude of +0.5 and an illuminated fraction of 35% at this time, and should be visible just above the east-north-eastern horizon at dawn, with Aldebaran and the Hyades Cluster 2° to its lower right. By month's end, Mercury is a little brighter and sits 6° above the horizon 45 minutes before sunrise.
- Mars passes behind the Sun (superior conjunction) on the 14th, so it is not visible this month.
- Venus brightens from magnitude -4.4 to -4.6 this month, dominating the western sky after sunset. It reaches elongation on the 6th, when it is 45.5° from the Sun in the eastern part of Gemini. At the beginnings of June, it appears about half an hour after sunset, 29° above the horizon. It grows from 22 to 32" during the month, while its illuminated fraction drops from a gibbous 53 to a crescent 34%. It is 19° above the horizon at sunset at the end of the month, setting around 23:35 BST (British Summer Time, 1 hour ahead of Universal Time) from the UK.
- This month is a good time to observe Saturn, as it is due south and at its highest not long after dark. To find it, follow the Plough's handle downwards to the orange star Arcturus, then continue to the white star Spica in Virgo. Saturn is a little brighter and yellower than Spica, and lies to its lower left in Libra. Binoculars or a telescope should reveal Saturn's brightest moon, Titan, at magnitude +8.2, and a magnification of at least 25 times allows the planet's rings to be seen. Saturn is visibly flattened by its rapid rotation. It has bands on its surface, but their colours are muted. The outer A and B rings are separated by Cassini's Division, which should be visible in a telescope of 4 or more inches (10 centimetres) in aperture when the atmosphere is fairly still. Within them is the C ring, but this is harder to spot. The inclination of the rings increases with respect to Earth until May 2017, making them more visible than usual for the next few years.
- The globular cluster M13 in Hercules and the 'Double Double' in Lyra are easily seen with binoculars or a telescope this month. M13 appears as a fuzzy blob, and is the brightest globular cluster in the northern hemisphere sky. The Double Double consists of a pair of binary stars to the lower left of Vega, which looks like two stars in binoculars but four in a telescope.
- The latter part of June is a good time to spot noctilucent (or polar mesospheric) clouds. Seen in the north at the end of twilight, they are the highest clouds in our atmosphere and float some 50 miles (80 kilometres) above the ground. Normally too faint to see, they can appear when illuminated by the Sun a little while after it has dropped below the horizon as seen from the ground. Look for them on a dark, clear night, as the last daylight is draining from the northern sky.
- The June Lyrid meteor shower peaks on the night of the 15th-16th. The meteors appear to radiate from a point near the star Vega in Lyra. Although there will be probably be only about 8 visible meteors per hour, the very thin crescent Moon does not obscure viewing.
- Venus lies close to the Beehive Cluster (M44) in Cancer on the 12th and 13th.
- The waxing gibbous Moon passes close to Saturn after sunset on the 28th. They are just over 1° apart when they set around 02:30 BST on the 29th.
- Venus and Jupiter, the two brightest objects currently in the night sky apart from the Moon, are just 21' apart on the 30th. Both are moving eastwards, with Venus catching up while the two are approaching the star Regulus in Leo. The planets have similar angular diameters at this time, around 32" each, but Venus is a crescent while Jupiter, because it is much further from the Sun than is the Earth, appears almost full. Though low in the west-north-west, they are very noticeable for about an hour from 22:30 BST.
Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during June 2015.
The winter solstice occurs on the 22nd (New Zealand Standard Time or NZST, 12 hours ahead of Universal Time) of this month, when the southern hemisphere is at its greatest tilt away from the Sun and the hours of daylight are at their shortest. The word 'solstice' indicates that the Sun is still, because it rises and sets at its most northerly points before moving south again. Brilliant Venus and golden Jupiter appear in the north-west after sunset, getting closer together as Venus ascends and Jupiter descends in the sky. They are joined by the crescent Moon on the 20th, and by the end of the month the two planets are less than one Moon diameter apart.
The centre of the Milky Way, in the constellation of Scorpius, rises high in the sky when seen from the southern hemisphere, and is currently midway up the eastern sky in the evening. The winter constellations of Scorpius and Sagittarius will dominate the night sky over the next few months. The red giant star Antares marks the heart of Scorpius, the Scorpion, and a near-vertical line of stars to its left represents the Claws. Saturn, at magnitude +0.8, is a little further left still, with an almost-full Moon passing within 1.5° of it on the 2nd. Scorpius is known to Māori as Te Matau a Māui, the Fish-hook of Māui. The mythical figure Māui used this to pull a giant fish from the ocean, which became Te Ika-a-Māui, the North Island of New Zealand. Antares is called Rehua, representing a drop of blood from Māui's nose that he used as bait. Scorpius was an important navigation aid in the South Pacific, as it moves overhead and shows the directions of east and west that would bring sailors to Aoteroa (New Zealand). Below the Fish-hook, the brightest stars of Sagittarius make the shape of an upside-down Teapot, and many star clusters and nebulae line the Milky Way in this part of the sky. M7, an open star cluster visible to the naked eye, sits about halfway between the stinger of the Scorpion and the spout of the Teapot. The nearby Butterfly Cluster, M6, is a lovely sight in binoculars.
The Māori new year, Matariki, happens this month when the Pleiades star cluster, also called Matariki, rises at dawn. Scorpius is on the west-south-western horizon at this time of year, with the Fish-hook pointing upwards, and Orion the Hunter is on the opposite side of the sky, rising due east. The three stars of Orion's Belt, known as Tautoru, line the horizon, and point to Sirius on their right. Sirius is called Takarua, and is the brightest night-time star. Following the Belt left leads to the V-shaped head of Taurus the Bull, with the orange star Aldebaran marking his Eye, and then to Matariki as it rises in the east-north-east. The Pleiades disappear from the sky in April, and their reappearance in early June indicates that the new year is approaching, with the next New Moon (or, in some areas, the next Full Moon) marking the actual turn of the year. This month, the New Moon happens on the 17th. Matariki, Tautoru, Takarua and Rehua are the four points of a celestial compass used to navigate the Pacific Ocean, with Matariki and Takarua marking the extremities of the Sun's rising points, Tautoru placed at one end of the celestial equator (the star Altair being at the other) and the Sun and planets moving along the line between Matariki and Rehua. They are also the four pillars, or Pou, holding up the Sky Father, Ranginui or Rangi, in Māori lore.
Odds and Ends
An unusual Wolf-Rayet star, with the unfortunate nickname of Nasty 1, could be an insight into the formation of these unusual stars. Wolf-Rayet stars are massive stars that have lost their hydrogen envelope, exposing their fusion core. Nasty 1 has been caught by the Hubble Space Telescope during a brief stage in which a companion star is stripping it of its hydrogen. The process is rather inefficient, and forms a huge pancake-like disk of gas 2 trillion miles wide (that’s a sixth of the way between the Sun and Proxima Centauri). It is thought that this may be a glimpse into the way Wolf-Rayet stars form.
Scientists using the Mars Reconnaissance Orbiter have found what appear to be long thin flows of salty water on the surface, one of which is fairly close to the Curiosity rover. The find raises questions over planetary protection, and how much we should interfere with possible life-bearing environments on other planets.
The Planetary Society is a nonprofit organisation dedicated to the development of future space technologies, exploration, education and of citizen space programs. It is currently involved with a project to demonstrate the proof-of-concept of solar sails, called the lightsail mission. The first phase of the mission, to test the deployment mechanism of the sail, was due to begin last week, however a software glitch has rendered the tiny satellite (known as a cubesat) incontactable, and now the team await a passing particle to reboot the system (which is not as rare as you'd expect)! The cubesat is currently chilling in a low-earth orbit, and you can find the full story here, or to follow the mission's updates live, check out this page. And if you want to get involved, why not take a look at the mission's Kickstarter page?
|Interview:||Dr. Debora Sijacki and Indy Leclercq|
|Night sky:||Ian Morison and Claire Bretherton|
|Presenters:||Charlie Walker, Indy Leclercq and Hannah Stacey|
|Editors:||Charlie Walker, Indy Leclercq and Mark Purver|
|Segment Voice:||Iain McDonald|
|Website:||Indy Leclercq and Stuart Lowe|
|Website:||Indy Leclercq and Stuart Lowe|
|Cover art:||An artist's impression of a disk of gas surrounding a Wolf-Rayet star which is being 'cannibalised' by a smaller companion star. This is the scenario envisaged for the NaSt1, or 'Nasty', star. CREDIT: NASA/ESA/G. Bacon (STSci)|