In the show this time, we talk to Dr. Rowan Smith about star formation in the early and recent universe, Ian rounds up the latest news, and we find out what we can see in the March night sky from Ian Morison and Claire Bretherton.
In the news this month, solar system buzzed by dwarf star, BICEP2 bubble bursts and Ceres shows some mysterious spots.
Astronomers revealed the startling discovery this month that the solar system received a close visit from a binary star system a mere 70,000 years ago, well within human history.Using telescopes in South Africa and Chile, a group of astronomers led by Eric Mamajek of Rochester University investigated the motion of the object WISE J072003.20-084651.2, more popularly known as Scholz's star.
Actually a binary system of two stars, the object was discovered by Ralf-Dieter Scholz in data from NASA's WISE (or Wide-field Infra-Red Survey Explorer) mission in late 2013. Interest was piqued due to the relatively close distance to us and the observation that it was apparently moving with almost no tangential velocity (i.e. side to side motion on the sky).By measuring the Doppler shift of the light coming from the star system, the team of astronomers was able to infer it was moving away from us, at great speed.
They then simulated a large number of potential orbits consistent with the system's current position and motion, finding that nearly all showed it passing through the Oort Cloud, a group of tiny, icy planetesimals which exist at the Solar System's extreme limits, at more than 100 times the distance to Neptune. Coming within 0.8 light years of Earth, this passage occured extremely recently (so far as the Universe is concerned), around 70,000 years ago, just as early humans were beginning their first migrations from the African continent. Unfortunately early astronomers would not have been aware of the close passage of Scholz's star as it consists of a tiny red and brown dwarf pair, both less than 10% of the mass of the Sun and even at the point of closest approach would not have been any brighter than 10th magnitude, making it around 50 times fainter than can be seen with a human eye. Such a close flyby could still represent problems for Earth, however, as it can perturb the orbits of larger objects in the Oort Cloud and send them towards the inner Solar System. The simulations of Mamajek and colloborator Scott Barenfield showed that there was only around a 1 in 10,000 chance that this could happen in the case of Scholz's star. Such close approaches are relatively rare, with the next comparable event being the possible passing of the 'rogue star' HIP 85605, between 250 and 500,000 years from now.
Also this month, cosmologists received the disappointing, if not unexpected, news that last year's much-lauded apparent detection of primordial gravitational waves by the BICEP2 experiment has been confirmed as a false positive. The previously claimed detection was met with much excitement as it would have represented extremely strong evidence in favour of 'inflation', the widely-supported theory that at very early times the entire Universe expanded at an exponential rate, blowing the tiniest quantum fluctuations up to the size of the observable Universe and providing the seeds for all the structures we observe today. This detection was in the form of B-mode polarisation of the Cosmic Microwave Background light. This particular swirl in the pattern of this first light to exist in the Universe has long being regarded as a smoking gun signature of inflation.
Unfortunately, as in so much of astronomy, the size of this effect is expected to be tiny and there are other unrelated physical effects which can mimic it. In the case of BICEP2's gravitational waves, this pesky contaminant was magnetised dust floating around inside our own galaxy, which is also capable of creating the B-mode swirl in the sky. When originally claiming their detection, the BICEP2 team had access to information from only one observational wavelength, meaning they were unable to separate the wavelength-dependant dust signal from the wavelength-independent inflation signal. They instead appealed to the assertion that the region of sky they were looking at was comparatively free of dust and its effect could hence be ignored. The Planck satellite showed otherwise. Whilst Planck cannot see as sharply as the South pole-based BICEP2, it has the advantage of looking at the entire sky in multiple frequency channels, enabling it to get a much clearer handle on the presence of dust. Astronomers' belief in the BICEP2 detection was always slightly wobbly and was shaken further late last year, when Planck released a map showing many regions of the sky were far dustier than previously expected. The denoument finally came from work leading up to this month's research paper, in which the previously notoriously secretive Planck team agreed to combine their data with that of the other team's BICEP2 and KECK experiments.
This combination of data appears to confirm that the previously seen signal was indeed dust and that no gravitational waves from inflation have been detected. The saga has provoked much introspection in the astronomical community on the relative merits of releasing early results and generation of widespread publicity as was the case for BICEP2. There is still cause for optimism, however. The new result puts a new upper limit on the amount of gravitational waves which could have been produced by inflation, disfavouring some previously popular models.And future experiments will aim to make the necessary more sensitive detection, with the balloon-borne SPIDER experiment making its first flight in January, with data now being analysed.
And finally the dwarf planet Ceres gave astronomers a surprise this month when a second bright spot appeared on its suface. Ceres is the largest object we know of - in the asteroid belt between Mars and Jupiter and has been imaged by NASA's Dawn spacecraft, which was despatched in 2007 to study the largest objects in the asteroid belt. As Dawn has approched Ceres it has been able to capture sharper images, showing that the previously known about single bright reflective spot was in fact two, appearing at the bottom the same crater basin on the dwarf planet's surface. Astronomers currently have no concrete evidence as to what these reflective spots could be, but have suggested they could be the result of geological processes erupting chemicals such as water, ammonia or methane and forming a so-called cryovolcano. From the 6th of March, Dawn will enter into an orbit around Ceres, gathering more data and hopefully telling us more about the odd, shimmering blotches.
Interview with Dr. Rowan Smith
Dr Rowan Smith has just started working at the University of Manchester and focuses on theoretical star formation. She talks to us about how she creates simulations of the formation process, and will be looking to compare these with real data to test if they are correct. Rowan explains how early stars differ from those born more recently and the contrasting initial conditions between them. She also delves into the physics of how star formation begins, expanding on how a suitable environment is created for stars to be born and the shape that such an environment takes.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during March 2015.
Orion, Taurus, Gemini and Canis Major are setting in the west in the evening. Gemini is the highest of these, with its bright stars Castor and Pollux representing the Heavenly Twins. Further east is Cancer, whose Beehive Cluster can be seen with binoculars and which is currently home to the planet Jupiter. Further over still is Leo the Lion, with its bright star Regulus. Botes, containing the star Arcturus, is rising in the east. The Plough, an asterism within Ursa Major, is high overhead, its back two stars, Merak and Dubhe, pointing towards Polaris, the North Star. Capella, the yellow star in Auriga, is also high in the sky.
- Jupiter reached opposition (opposite the Sun in the sky) on the 6th of February, and is still high in the south late in the evening. During March, it dims from magnitude -2.5 to -2.3 and shrinks from 44.5 to 41.6", as it moves retrograde (westwards) towards the Beehive Cluster in Cancer. A small telescope allows you to see the equatorial bands, the Great Red Spot (at certain times) and the four Galilean moons.
- Saturn is in Scorpius, near the leftmost star of the fan representing its head, and rises at around midnight UT (Universal Time) at the end of March. It grows from 16.9 to 17.8" during the month, as it brightens in magnitude from +0.4 to +0.3. Though no higher than 22° when visible in the UK and therefore subject to significant atmospheric distortion, it is high enough in the south-south-east before dawn to make out its ring system using a small telescope, as this is now some 25° from our line of sight. Saturn switches from eastward to westward motion relative to the stars around the 11th.
- Mercury sinks into the Sun's glare at the beginning of March, so is is not a good month to observe it.
- Mars starts the month on the boundary of Pisces and Cetus, before moving eastwards and entering Aries on the 30th. It dims from magnitude +1.3 to +1.4 during March, while its disc shrinks from 4.3 to 4". It is best seen about 15° above the western horizon as darkness falls. It is just 18' above Uranus on the 11th.
- Venus has become an evening object, appearing higher above the horizon each night. Shining at magnitude -4, it dominates the western sky an hour after sunset. Its angular size increases from 12 to 14" over the month, and its illuminated fraction wanes from 86 to 78%, but it still appears blurred by atmospheric turbulence due to its relatively low elevation.
- A partial solar eclipse is visible across the UK at around 09:00 UT on the 20th. It is total in some places between Scotland and Iceland, such as the Faroe Isles. To avoid damaging your eyes, don't look directly at the Sun unless you are wearing dedicated eclipse glasses. Alternatively, project an image of the Sun by making a pinprick-sized hole in a piece of foil and allowing the sunlight to shine through it into a dark hollow such as a shoebox.
- Venus and Mars lie close together after sunset from the 1st to the 7th, with Uranus about halfway between them at the end of this period.
- Venus and Uranus are just 6' apart in the sky on the 4th. Venus, at magnitude -4, is some 10,000 times brighter than Uranus, which requires binoculars to be seen at magnitude +5.9. In order to see the fainter object, you may need to use a telescope and eyepiece with high magnification, so that you can move Venus out of the field of view.
- Mars is just 2° from a waxing crescent Moon after sunset on the 21st, low above the western horizon.
- Venus is only 3° from the waxing crescent Moon on the evening of the 22nd.
Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during March 2015.
The evenings are drawing in as the autumnal equinox passes on the 21st. The summer constellations of Canis Major, Orion and Taurus are in the north-western evening sky. The brightest star in the night sky, Sirius - Takurua to Māori - is almost overhead, with Rigel and Betelgeuse below. Between them is Orion's Belt, three stars that are known as Tautoru in New Zealand. It points down through the head of Taurus the Bull, which contains the Orange star Aldebaran as the Bull's Eye. This V-shape also hosts the Hyades Cluster. For observers with binoculars or a telescope, over 100 stars brighter than 9th magnitude can be seen. Below the V and near the horizon is the Pleiades Cluster, representing the half-sisters of the Hyades in Greek mythology. Called Matariki in New Zealand, their first pre-dawn rising each June marks the Māori New Year.
The second-brightest night-time star, Canopus, is high in the south-west, with the blue star Achernar slightly below. The two of them form a near-equilateral triangle with the south celestial pole, around which the sky appears to rotate. Although this point lacks a nearby bright star, the constellation of Crux (the Southern Cross) helps to locate it. High in the south-east in the evening, Crux is accompanied by the Pointer Stars, Alpha and Beta Centauri. To find the pole, point one hand at Gamma Crucis, the star at the short end of the Cross, point the other hand at Achernar and then bring the two hands together in the middle. This should point you south.
The two dwarf galaxies known as the Magellanic Clouds are visible to the naked eye as two fuzzy patches near to the south celestial pole. Each contains billions of stars, and the Large Magellanic Cloud is the higher of the two. Binoculars or a small telescope can pick out some of its star clusters as individual patches of light within it. A bridge of gas connects it to the Small Magellanic Cloud, demonstrating tidal interaction between the two. It is easiest to spot them around New Moon on the 20th, when they are high in the south after dark.
- Jupiter dominates the northern sky this month, setting in the north-west in the early hours of the morning. The Moon passes close by on the 3rd and 30th.
- Venus appears briefly at dusk, low in the west. It sets about an hour after the Sun at the start of the month, rising to 1.5 hours by the end. In the middle of next month, it will begin to remain visible until after twilight.
- Saturn rises in the east before midnight NZDT (New Zealand Daylight Time, 13 hours ahead of Universal Time) at the beginning of March, and before 22:00 at the end. It sits just below the Claws of Scorpius the Scorpion, which is a winter constellation known as Te Matau a Māui to Māori. This represents a mythological hook that was used by Māui to catch a large fish that became the North Island of New Zealand. The red star Antares is higher and further south than Saturn, and represents the Scorpion's Heart - to Māori this is Rehua, a drop of blood from Māui's nose that he used as bait for the hook. A small telescope reveals Saturn's rings and its largest moon, Titan. Titan is the only known moon with an atmosphere, and the only body in the Solar System - apart from the Earth - with liquid lakes on its surface, although these consist of methane rather than water. Our own Moon appears close to Saturn on the 12th.
- Mercury is coming to the end of its best morning apparition of the year. It rises in the east around 05:00 NZDT at the beginning of March, but becomes lost in the morning twilight by the end as it appears less than an hour before the Sun.
Odds and Ends
Leonard Nimoy passed away on 27 February at the age of 83. While Nimoy was best known for his portrayal of Spock on Star Trek, he also narrated science-related videos such as the 2007 NASA video on the Dawn Mission and the short documentary The Once and Future Griffith Observatory on the history of Griffiths Observatory. He also donated the funds for the Leonard Nimoy Event Horizon Theater at Griffiths Observatory, and he was actively involved in promoting science and space exploration. In the 1970s, the influence of Star Trek was so strong that a write-in campaign to NASA prompted the organization to name the first prototype Space Shuttle Enterprise after the spacecraft in Star Trek, and many of the cast members form Star Trek, including Nimoy, appeared at early promotional events for the shuttle program. Many astronauts, scientists, and engineers have cited Star Trek and Nimoy as inspirations for why they became involved in space science. More information on Leonard Nimoy's influence on science can be found in the Space.com article, the statement from NASA, and the Washington Post blog post on his passing.
Astronomers announce the discovery of the brightest quasar yet discovered. It has a luminosity of 420 trillion Suns, and the supermassive black hole that powers it is estimated to have a mass of 12 billion solar masses. The quasar, designated SDSS J0100+2802, has a redshift of 6.3 which means it formed only 900 million years after the Big Bang. The findings may support ideas that black holes grew faster than their host galaxies in the early universe, and will help astronomers understand how galaxies form and evolve through cosmic time. The findings were published in the journal Nature, and you can read more about the story here.
Buzz Aldrin and two other astronauts testified in front of the U.S. Senate's Subcommittee on Space, Science and Competitiveness as to the importance of an American programme to establish a colony on Mars. Aldrin laid out a vision of how to get there by the year 2038, involving the use of a robotic cycler and 'leveraging asteroid rendezvous' to provide a reliable link to and from the Red Planet. All three astronauts spoke for the benefits to humankind of manned missions to Mars, while acknowledging that at current levels of funding, NASA would face a difficult task ahead.
In a somewhat related event, SpaceX's Falcon 9 rocket launched its first dual-satellite payload, delivering two fully electrically driven telecommunications satellites to Earth orbit. The satellites employ electric ion thrusters, accelerating Xenon ions for propulsion. The launch marks a step into commercial viability and widespread use of these engines, which add less weight to the payload at the expense of slower velocities.
|Interview:||Dr. Rowan Smith and Josie Peters|
|Night sky:||Ian Morison and Claire Bretherton|
|Presenters:||George Bendo, Indy Leclercq and Hannah Stacey|
|Editors:||Adam Avison, Monique Henson, Mark Purver and Charlie Walker|
|Segment Voice:||Tess Jaffe|
|Website:||Indy Leclercq and Stuart Lowe|
|Cover art:||An artist's impression of the most distant quasar yet discovered, at a similar distance to SDSS J0100+2802, the brightest distant quasar found so far CREDIT: ESO/M.Kornmesser|