More bees than a Proxima hive. In the show this time, we talk to Dr. Francesco Shankar about AGN, Ian rounds up the latest news, and we find out what we can see in the September night sky from Ian Morison and Claire Bretherton.
In the news this month: a planet orbiting Proxima Centauri, tree rings and solar storms, and a table-top black hole.
This month the scientists at the European Southern Observatory (ESO) revealed the discovery of an exoplanet orbiting Proxima Centauri, the closest star to Earth other than the Sun. The newly discovered planet is the first one known in the Proxima Centauri system, has been named Proxima b and is a mere 4.2 light years (or 40 trillion kilometres) away from us here on Earth. In an article published in Nature, a team led by Dr Guillem Anglada Escude of Queen Mary University in London, described how the planet was initially detected and confirmed by the Pale Red Dot project. By making incredibly precise measurements of the motions of the host star with the HARPS spectrograph, the astronomers were able to see the star wobbling as the planet orbited. In star-planet systems, like any many-body system, all objects affect each other, meaning as well as the massive star in the centre pulling on the outer planets and causing them to orbit, those planets too exert a pull back on the star. This means that rather than all orbiting the centre of the central star, the bodies in the system in fact all orbit a common point known as the barycenter.
In our own solar system, the complex gravitational interactions of the Sun with the eight planets means the barycentre follows a convoluted spiral pattern with a centre which is sometimes inside the Sun (meaning it merely wobbles) and sometimes outside (meaning the Sun actually has its own very small orbit). By tracking the motions of Proxima Centauri, the Pale Red Dot team were able measure the wobble of the star caused by the orbiting planet, which in turn allowed them to infer some of Proxima b's properties, including the mass and orbital radius.
Proxima b has caused much excitement. Not only is it the closest exoplanet ever discovered, but it also has the possibility to be an Earth-like planet in its host star's habitable zone. Weighing in at between 1.3 and 3 Earth masses, Proxima b has the right mass range for a rocky planet and also lives at a distance from its parent star which means its Planetary Equilibrium Temperature -- the temperature it would have from only considering heating by the star -- is a mild 234 Kelvin (compared to 255 K for Earth). This is just -39 degrees centigrade and means with the correct atmospheric composition to give a greenhouse effect the conditions may be right for liquid water on the surface. However, these are just possibles: whilst we know the mass range, we do not know the composition of Proxima b, which could be either rocky like Earth or gaseous like a miniature Neptune. And in addition, anyone planning on making the trip to Proxima b may want to think twice. The star Proxima Centauri is not like our Sun, but is a Red Dwarf -- a long-lived star which is much smaller and cooler. This means that Proxima b is very close to the star -- only 5% of the distance from the Earth to the Sun -- and years on Proxima b last only 11 Earth days. Such a short orbital period means Proxima b is almost certainly tidally locked, with one side of the planet continually facing towards the star and one away. And, even worse, Proxima Centauri is an extremely active regularly flaring star, increasing in brightness by up to 50% several times per year. These flares give out huge amounts of X-rays, which could cause significant damage to any life and indeed any atmosphere on Proxima b. Even if chances for habitability may look small, Proxima b is still a great find, showing yet again the frequency and variety with which extrasolar planets occur.
We may even be able to send a probe to Proxima b, with the Breakthrough Starshot project suggesting it as a destination for one of their tiny, solar-sail powered craft. Travelling at roughly 20% of the speed of light, one of these probes could reach and send signals back from Proxima b about 30 years after launch, with the current aim of a first mission in around 2036. This may seem long term, even to astronomers used to decades-long projects, but is something I would definitely be willing to wait for.
- Also in the news this month, the coinage of a new science was made in astrochronology -- the use of evidence of solar storms visible in tree rings to date historical events. Humanity's previous best way of dating events over the past few millennia has been through radiocarbon dating. When organic matter dies, it ceases to absorb the Carbon-14 isotope from the atmosphere. The Carbon-14 then slowly decays, whilst the stable Carbon-12 isotope does not, meaning the Carbon-14/Carbon-12 ratio can be used to date the organisms death -- and subsequent use by humans as food, writing or building material and so on. Unfortunately this radiocarbon dating is only so accurate, as the amounts of Carbon-14 in the atmosphere vary, both in time and regionally across the globe, meaning most dates are only good to a range of one to two hundred years. This means that many historical records of ancient societies are not 'anchored' to the Gregorian calendar used in the West today. The first confirmed absolute date in the European calendar is 763 BCE, in the Chinese calendar is 841 BCE, and in the Americas is only the arrival of Columbus in 1492. Civilisations with sophisticated calendars and record keeping such as Mayans, Assyrians and Egyptians existed long before these dates, but we do not know exactly where these chronologies fit relative to each other and to our own, floating around with error bars of up to a few centuries.
In work by Oxford University archaeologist Michael W. Dee and astrophysicist Benjamin Pope, a radical new way of anchoring these timelines is proposed. The new source of information comes from Miyake events, first described in 2012, which are large, sudden increases in the amount of Carbon-14 in the atmosphere, thought to be almost certainly from large energetic solar events such as solar flares. These Miyake events can be dated as they are also visible in tree-ring records, where the new annual growth of bark can be seen in the cross-section of a tree trunk. Given a successfully calibrated tree ring record -- many of which exist, Miyake events can then be associated with a single year of occurrence, with two so far known in 775 and 994. Because Miyake events are short lived and global, these spikes in Carbon-14 can now be used to precisely date any organic matter used by societies in those years. Non-Miyake variations in Carbon-14 are comparatively slow, meaning if large variations in the Carbon ratios are observed across objects which are otherwise known to be around the same relative date, a precise absolute date can now be given, with Dee and Pope focusing on the use of a good mathematical tool -- Gaussian Processes -- for detecting these sudden jumps in Carbon-14.
If previously floating chronologies can be anchored, there is much to learn, with the data potentially helping us understand how ancient civilisations rose, fell and interacted with one another.
And finally, a scientist published results from a table-top black hole this month. Rather than being a true black hole, an object so massive even light cannot escape its gravitational pull, instead the model black hole consisted of a condensate of ultracold atoms, with sound waves trapped inside. The goal was to model the emission of Hawking radiation from a black hole. According to Stephen Hawking's seminal work from the 1970s, the pairs of virtual particles which are constantly popping in and out of the vacuum of space are occasionally separated by the event horizon of a black hole. One particle falls in, never to return and the other escapes, making the transition from virtual to real.
By cooling Rubidium atoms into a Bose Einstein Condensate -- in order to make their quantum behavior readily visible -- physicist Jeff Steinhauer of the Technion-Israel Institute of Technology in Haifa was able to trap quanta of sound, known as phonons. By creating entangled pairs of phonons and then accelerating the super-cooled atoms, Steinhauer created an analogy to a black hole event horizon and confirmed, in principle, that it is possible for something which looks like Hawking radiation to exist. There are, of course, a few caveats to the work: it relies on the atoms being in a true Bose Einstein state, and has so far only been able to generate entangled phonons at relatively high energies. And, theorists may look askance at the usefulness of the imperfect analogy -- Leonard Susskind of Stanford University in California pointing out that the system lacks a key feature of black hole systems which makes Hawking radiation such an important concept in physics, it will not evaporate. The evaporation of black holes and the question of what happens to the information from the pair particles lost inside them forms the basis of the black hole information paradox, the solution to which is regarded as a key component in any future theory which unifies quantum mechanics and general relativity.
For now, though, the result remains an impressive technological feat and an excellent piece of incongruity: a black hole in a basement.
Interview with Dr. Francesco Shankar
Dr Francesco Shankar is a lecturer at the University of Southampton where he researches the co-evolution of supermassive black holes and their host galaxies. Dr Shankar talks to Alex about how we can use the dynamics of the stars and gas towards the centre of galaxies to infer the masses and properties of the black holes that lurk in their centres and what this tells us about how star formation and black hole growth are co-dependent on one another.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during September 2016.
To the south and moving westward as night progresses you may see the Summer Triangle: the bright stars Deneb (in Cygnus), Vega (in Lyra) and below them Altair (in Aquila). Towards the south later in the evening you may spot the great square of Pegasus - adjacent to Andromeda and M31, the Andromeda Nebula. To the north lies "w" shaped Cassiopeia and Perseus. Between the two, close to the Milky Way, try to spot the Perseus Double Cluster with a goods pair of binoculars. You might also spot M33 may also be visible on a transparent night with a good pair of binoculars.
- Jupiter reached superior conjunction on August 26th, and now rises shortly before the sun. It will be best seen at month's end, 18 degrees above the northeast horizon at sunrise. With a disk increasing to 31 arcsecond disk, you should be able to see its equitorial bands and 4 Galilean moons.
- Saturn can be seen after sunset low in the southwest. It lies in eastern Libra, moving slowly away from the wide double star Alpha Librae as it shines with a magnitude of +0.6. One hour after sunset at the start of the month it will lie just 10 degrees above the horizon with a 16.4 arc second disk. By month's end it will only be a few degrees elevation at this time so early this month is really our last chance to observe it for a month or so as it passes behind the Sun. The ring system, now opened out to 24.3 degrees to the line of sight, should still be visible along with Titan, its largest satellite.
- Mercury can be seen just above the western horizon for the first few days of the month reaching greatest elongation from the Sun on the 4th of September shining at magnitude +0.1. It will be lost in the twilight by mid-month before it passes in front of the Sun (Inferior Conjunction) on the 30th.
- Mars is a pre-dawn object, and lies in Leo not far from Regulus, Alpha Leonis. On the 25th the salmon-pink planet will lie just 47 arc minutes from the blue star making a very nice colour contrast. Shining at magnitude +1.8 its disk is just 3.8 arc seconds across so no details will be seen of its surface. Seen best towards the end of the month, it will then rise around 3 hours before the Sun.
- Venus, rises in the east-northeast in the pre-dawn sky an hour and a half before the Sun at the start of September but this increases to four hour by month's end as Venus moves further away in angle from the Sun. Shining at a magnitude -4.8 during the third week of the month month it will show a thin crescent, 9% illuminated, 52 arc second disk as the month begins.
On September 4th and 21st you may spot The Alpine Valley, a cleft across the Appenine mountain chain. It is about 7 miles wide and 79 miles long and a thin rill runs along its length which is quite challenging to observe.
- Neptune came into opposition on the 29th of August, so will be seen well this month. Its magnitude is +7.9 so Neptune is easily spotted in binoculars lying in the constellation Aquarius as shown on the chart. It rises to an elevation of ~27 degrees when due south. Given a telescope of 8 inches or greater aperture and a dark transparent night it should even be possible to spot its moon Triton.
- Look east before dawn on 5th September: the magnitude +0.9 star Aldebaran will be occulted by the bright limb of the Moon as it passes in front of the Hyades cluster at around 05:30 BST. Given a mount tracking Aldebaran with a telescope, you may see it reappear from behind the unlit lunar disk at 07:10 in the bright daylight sky. Be warned: the times will vary by a few minutes depending on where you live in the UK so be watching Aldebaran for perhaps 10 minutes before the two stated times.
- All clear before dawn on 10th September given a good low unobstructed horizon towards the northeast you may spot an 8% lit, thin crescent Moon just 2 degrees to the upper left of Venus shining at magnitude -4.6.
- Looking southwest one hour after sunset on 18th September (20:45 BST), Saturn will be seen 4.5 degrees to the lower left of a waxing crescent Moon.
- About one hour before dawn on the morning of the 25th, Mars will be seen less than one degree just to the left of Regulus in Leo. Shining brightly up to their right will lie Venus, dominating the morning sky whilst lying well below Mars will be seen Jupiter - a very nice planetary grouping.
- Before dawn on 28th September, from 01:12 BST until 06:22 BST we will witness a total eclipse of a Harvest Supermoon! It will display the largest apparent angular diameter of the year (33.5 arc minutes) and the eclipse lasts for three hours and twenty minutes with totality starting at 03:11 BST and ending at 04:23. At the mid point of the eclipse at 03:47 BST the Moon will then lie at an elevation of 27 degrees above the southwest horizon. As the Moon leaves the umbral shadow 05:27 BST it will lie some 15 degrees above the horizon in the dawn sky.
Claire Bretherton from the Space Place at Carter Observatory in New Zealand speaks about the southern hemisphere night sky during September 2016.
Kia Ora and welcome to the September Jodcast from Space Place at Carter Observatory, here in Wellington , New Zealand.
It's hard to believe that it's now a year since the birth of my daughter, Seren (whose name means star in Welsh, by the way) so after taking some time out to spend with her I'm back to pick up the reigns of the southern night sky jodcast. Huge thanks to Haritina for doing such an amazing job in my absence.
September marks the start of spring here in the southern hemisphere, and as we head towards the equinox on the 23 rd , our days begin to lengthen. Sunset and sunrise times change rapidly at this time of the year, with the Sun dipping below the horizon an hour and a half later at the end of the month than at the beginning. By the end of September the Sun won't be setting until nearly half past 7. Whilst we're looking forward to some better weather, this will also mean fewer hours of darkness to get out and observe our Southern skies.
All five naked eye planets continue their planetary dance this month. Jupiter, Mercury and Venus begin the month close together above the Western horizon after dark. Venus is the brightest and the highest of the three, easy to spot, even in the twilight sky. Jupiter, with its golden glow is below with fainter Mercury to the left. Mercury slips quickly into the twilight sky, with Jupiter following by mid-month. After passing between us and the Sun, Mercury will make a morning appearance during late September, but won't be rising until twilight is well underway, making it very difficult to spot.
Venus moves quickly up away from the other two, passing up to the right of 0.9 Magnitude Spica around the 19 th of the month. By the end of the month it will be setting over 2 and a half hours after the Sun.
Mars and Saturn still form a triangle with Antares, high in the northern sky after dark. Saturn is almost directly below Antares, and the two remain close together throughout the month gradually dropping lower in our evening skies and setting by around midnight at the end of September. Mars, the brightest of the three, begins the month just to the right of Saturn and Antares, but holds its position in the sky as it moves eastwards against the background stars, drifting up and to the right away from Saturn as the month wears on.
The bright stars Canopus and Vega mark north-south after dark this month. Canopus is the second brightest star in the night time sky, and the brightest in the southern constellation of Carina, the keel. Carina was once part of the great ship Argo Navis, which sails across the southern skies. In 1752, the French astronomer Nicolas Louis de Lacaille split Argo Navis into three smaller constellations of more manageable size: Carina (the keel), Puppis (the poop deck, or stern), and Vela (the sails).
To Maori Canopus is known as Atutahi or Autahi, meaning "stand alone" because of its isolated position outside the band of the Milky Way. Canopus represents the ariki, or high chief of the heavens, and is circumpolar here in New Zealand, always visible in our night time skies.
Vega, in the constellation of Lyra, is the fifth brightest star in the sky, and at just 25 light years away, one of the brightest in our local neighbourhood. It is also one of the best studied, and was the first star outside our Sun to be photographed in 1850. Vega is also extensively used by astronomers for photometric calibration. It is used as a zero point to define the UBVRI photometric system first introduced in the 1950s, and extended in the 1970s, to classify stars according to their colours.
Along with the nearby bright stars of Deneb, in Cygnus the swan, and Altair, in Aquila the eagle, Vega forms part of the "winter triangle" as seen here in the southern hemisphere. Altair is easy to spot, lying along the band of the Milky Way, midway up the northern sky after dark. Deneb is harder to see, just skirting along the horizon from northern parts of the country.
Between Vega and Altair is Albireo, or Beta Cygni, the beak star, marking the head of the swan. Although it appears as a single star to the naked eye, Albireo is in fact a double star and a lovely sight in a small telescope because of the easily seen contrast in colour between blue and gold components. The two stars are 35 arcseconds apart, meaning they are separated by 60 times the diameter of our Solar System, and may take 100,000 years to orbit each other.
The brighter magnitude 3 yellow star has also been found to be a binary star in its own right, but a much larger telescope and excellent observing conditions, or complex image processing, would be needed to resolve it.
Albireo is best viewed using low magnification, as the colours stand our more clearly when the stars appear close together. You might also try de-focussing your telescope a little to spread out the stars' light, making the colours easier to see.
A similar distance to the other side of Altair is Alpha Capricorni. Whilst it has the alpha designation, it is actually the 3rd brightest star in the zodiac constellation of Capricorn, the goat, and is commonly known as Al Giedi, meaning the kid. Alpha Cap is another double star, but this time the effect is purely coincidence.
Although these stars appear close together, their proximity is just a line of site effect, with the two components positioned at 109 and 690 light years away. Alpha-2, or Secunda Giedi is the closer and brighter of the two, a giant star with a luminosity around 40 times that of the Sun, and an apparent magnitude of 3.58. Alpha-1 or Prima Giedi is a supergiant over 5 times more distant, but at 5 times the mass and over 1000 times the luminosity of the Sun, it is only slightly fainter in our skies, at magnitude 4.3. Both are evolved G class yellow stars, at a similar temperature to our Sun, and Alpha Giediis a multiple star in its own right, with at least 3 faint companions nearby.
Prima and Secunda are located 6.6 arcminutes apart, around one fifth the diameter of the full moon, and can be separated fairly easily even with the naked eye.
As Haritina mentioned last month, the Milky Way is spectacular in our evening skies at this time of year, passing from Vega and Altair towards the north, through Sagittarius and Scorpius overhead, and down to the southern horizon, just to the west of Canopus. Midway up the southern sky you'll find Crux, the Southern Cross, with the pointers Alpha and Beta Centauri above.
Alpha Cen is another multiple star system, and at a distance of 4.37 light years, is the closest star system to our Sun. The two main components Alpha Cen A and B are both similar in mass and luminosity to the Sun and are close enough that they would fit within the orbit of Pluto. They are too close together to be resolved with the naked eye, but a pair of binoculars or small telescope will easily separate them.
The third component, Alpha Cen C, is a small, faint red Dwarf star, also known as Proxima Centauri, which can be glimpsed even in a small telescope. Lying 0.2 parsecs, or 15,000 AU from the AB pair, that's around 500 times the orbit of Neptune, Proxima Centauri's current distance of around 4.25 light years makes it the closest star to our Sun.
On 24 August, a team of astronomers led by Guillem Anglada-Escude, announced that they have discovered a potentially Earth-like planet orbiting around Proxima Centauri. The planet was identified using radial velocity measurements of its parent star. As the planet orbits it causes the star to wobble, and this wobble can be detected by measuring the Doppler shift in the stars spectrum.
Named Proxima b, the newly discovered planet takes just 11.2 days to orbit its star, putting it at 1/20 th of the distance from the Earth to the Sun, but, because Proxima is a much smaller, fainter star, the energy it receives is around 2/3 s the energy that reaches Earth, so Proxima b lies firmly in the habitable zone, the region of space where any water on the planet could be liquid. With a minimum mass of 1.3 times the Earth, this opens up an exciting possibility that not only have we found a planet around our nearest star, but that this planet may be Earth-like, and potentially, able to support life.
Wishing you clear skies from the team here at Space Place at Carter Observatory.
Odds and Ends
- Pulsars sometimes do strange things. They experience jumps in their spin-rate, their emission beams appear to change shape, they sometimes just switch off all together and if they're magnetars, are prone to throwing out occasional bursts of X-rays. PSR J1119-6127 recently underwent all of the above. We've been keeping an eye on this pulsar for a while as, although it's not technically classed as a magnetar, it does have an stronger than average magnetic field and has been known to show magnetar-like behaviour in the past. As well as radio, it's also visible in X-rays and gamma rays. On July 27th, Swift's Burst Alert Telescope noticed a strong burst of X-rays from the direction of this pulsar and slewed over to have a look, confirming that 1119 had undergone a magnetar-like X-ray burst. Swift followed up on this source a little later and noted that its X-ray pulsations had jumped up in energy from soft (< 2.5 keV) to hard X-rays. Careful timing of the X-ray pulses, showed that this pulsar had undergone a glitch in its spin-rate by around 10 parts per million - which is comparitively large for a glitch. As if that weren't enough interesting phenomena for a pulsar to exhibit in one episode, observations with the Parkes radio telescope showed that the radio pulses had gone! This is interesting for a number of reason as some think perhaps magnetars should not be considered a separate class of pulsar and in fact normal pulsars which have a strong magnetic field should show magnetar-like behaviour - that is, X-ray bursts coincident with large glitches. 1119 has certainly done this and more! Since it's tantrum, its radio emission has since returned but its emission beam is a different shape and strength. We expect we'll be watching this strange little object more closely for a while yet.
If you haven't heard enough about our new neighbour already, a rocky planet of 1.3 Earth masses has just been discovered residing in the nearest solar system to our own. Proxima b has the brisk period of 11.2 days and is 8 times closer to its parent star, Proxima Centauri, than Mercury is to our own Sun. However, it orbits a red dwarf star, which is much cooler and less luminous than the Sun, which means Proxima b has the potential to harbor liquid water on its surface. All is not rosy for any potential lifeforms on this planet, however, as Proxima Centauri is prone to X-ray and ultraviolet tantrums. But scientists have been doing their best to investigate its potential habitability, and are already considering what lifeforms native to extreme environments on Earth could thrive there.
Chris Walker, esarmen and Joseph Brimacombe have sent in photos on Facebook and Flickr respectively, so if you want to see some of the fantastic images that our listeners are taking of the night sky in both hemispheres, then you should definitely check them out!
|Interview:||Dr. Francesco Shankar and Alex Clarke|
|Night sky:||Ian Morison and Claire Bretherton|
|Presenters:||Charlie Walker, Mat Malenta and Benjamin Shaw|
|Editors:||Alex Clarke, Claire Bretherton, Monique Henson, Andy May, Benjamin Shaw and Charlie Walker|
|Segment Voice:||Iain McDonald|
|Website:||Charlie Walker, Minnie Mao and Stuart Lowe|
|Cover art:||The location of Proxima Centauri in the southern sky CREDIT: Wikimedia Commons|