Written by Megan Johnson, Post doctoral researcher in dwarf galaxies at CSIRO
Dwarf galaxies are the most abundant galaxies in the universe. Yet understanding how these systems behave in galaxy group environments is still a mystery.
These objects are notoriously difficult to study because they are very small relative to classic spiral galaxies. They also have low mass and a low surface brightness, which means that, to date, we have only studied the dwarf galaxies in the nearby universe, out to about 35 million light years away.
My collaborators and I have been studying a dwarf galaxy named ESO 324-G024 and its connection to the northern radio lobe of a galaxy known as Centaurus A (Cen A).
The giant radio lobes are comprised of high energy charged particles, mostly made up of protons and electrons, that are moving at extremely high speeds. The lobes were created from the relativistic jet (shown in the image at the top) that is blasting out of the central core of Cen A.
These energetic particles glow at radio frequencies and can be seen as the fuzzy yellow lobes in the centre of the image (above), together with the neutral hydrogen intensity (HI) maps of its companion galaxies. The lobes now occupy a volume more than 1,000 times that of the host galaxy shown in the image at the top, assuming the lobes are as deep as they are wide.
These HI intensity maps are part of a large HI survey of nearby galaxies called the Local Volume HI Survey (LVHIS). These maps have been magnified in size by a factor of 10 so that they can be seen on such a large scale and are coloured by their relative distances to the centre of Cen A.
A green galaxy is at virtually the same distance from Earth as Cen A, while blue galaxies are in front of Cen A (closer to us) and red galaxies are behind it (farther away).
One of the striking things about this image is that out of the 17 galaxies overlaid onto the Cen A field, 14 are dwarf galaxies.
An interesting dwarf
The one object that really interested me after making this image was the dwarf irregular galaxy ESO 324-G024 (just above the black box). It has a long HI gaseous tail that extends roughly 6,500 light years to the northeast of its main body and it is at nearly the same distance as Cen A.
These two pieces of information right away made this a system worthy of investigation because we thought that perhaps there is a connection between this dwarf galaxy and the northern radio lobe of Cen A.
Nothing like this has ever been seen before, probably because galaxies that have giant radio lobes like Cen A are usually hundreds of millions to billions of light years away. Cen A is a special galaxy because it’s only about 12 million light years from Earth.
This was an interesting result and it told us that the northern radio lobe must be inclined toward our line of sight, because ESO 324-G024 was at nearly the same distance as Cen A. This had previously been suggested by studying the jet way down in the core of the host galaxy, but it had never been confirmed in this way before.
A wind in the tail
Next we investigated the mechanism responsible for creating the HI tail in ESO 324-G024. We looked at the likelihood of gravitational forces from the large, central host galaxy of Cen A as a potential culprit for ripping out ESO 324-G024’s gas. But we determined that it is simply too far away from the central gravitational potential for gravity to have created the tail.
So we explored ram pressure stripping, which is thought to be a dominant force for removing gas in galaxies within these kinds of groups. Ram pressure is a force created when a galaxy moves through a dense medium, and thus experiences a wind in its “face”.
It’s similar to holding a dandelion in your hand and then running as fast as you can go and watching the seeds blow away in the wind. At rest, the dandelion feels no wind and the seeds stay intact. But when you run, all of a sudden, the dandelion feels the wind created from your running and this wind blows away the seeds.
In this scenario, ESO 324-G024 is the dandelion and you represent gravity carrying the galaxy through space. We calculated the wind speed required to blow the gas out of ESO 324-G024 and compared this speed to the speed of ESO 324-G024 moving through space. It turns out that the two speeds did not match.
ESO 324-G024 seemed to be moving too slow for all of its gas to have been blown into its long tail. So we went back to our first conclusion about ESO 324-G024 being behind the radio lobe and surmised what may be happening.
We know that the charged particles inside the northern radio lobe of Cen A are moving extremely fast. If ESO 324-G024 is just now coming into contact with the posterior outer edge of the radio lobe of Cen A, which is likely due to its proximity to Cen A, then it is possible that ESO 324-G024 is not only feeling the wind generated from its own motion through space, but also the wind from the charged particles in the radio lobe itself.
This would be like you running with the dandelion and at the same time blowing on it. Therefore, we concluded that ESO 324-G024 is most likely experiencing ram pressure stripping of its gas as it passes close to the posterior edge of the northern radio lobe.
This means that these types of radio lobes must have wreaked havoc on their dwarf galaxy companions in the distant past. This is an interesting case study that showcases how dwarf galaxies may have been knocked about, blasted, by their larger companion galaxies.
Just how common are situations like this and how have they influenced dwarf galaxies over cosmic time? The answer is that we simply don’t know, but I look forward to exploring these questions.
CSIRO has signed a multi-million dollar agreement to use its 64 metre Parkes radio telescope in the quest to search for intelligent life elsewhere in the universe.
Breakthrough Listen will be allocated a quarter of the science time available on the Parkes telescope from October 2016 for a period five years, on a full cost recovery basis.
The Parkes observations will be part of a larger set of initiatives to search for life in the universe. The ET hunters will also use time on the Green Bank telescope in West Virginia, operated by the US National Radio Astronomy Observatory, and a telescope at the University of California’s Lick Observatory.
CSIRO has the only capability for radio astronomy in the southern hemisphere that can deliver the scientific goals for the new initiative. The Parkes Radio Telescope is essential for the scientific integrity of the Search for Extraterrestrial Intelligence (SETI).
It is ideally situated for a search such as this. The most interesting and richest parts of our own galaxy, the Milky Way, pass directly overhead. If we are going to detect intelligent life elsewhere, it is most likely going to be found in that part of the galaxy towards the centre of the Milky Way.
The Parkes Radio Telescope is also one of the world’s premier big dishes and has outstanding ability to detect weak signals that a search like this requires.
It has always been at the forefront of discovery, from receiving video footage of the first Moon walk on 20 July 1969 (which was dramatised in the movie The Dish), to tracking NASA’s Curiosity rover during its descent onto Mars in 2012, to now once again searching for intelligent life.
It has also played a leading role in the detection and study of pulsars, small dense stars that can spin hundreds of times a second, the recent discovery of enigmatic (but boringly named) fast radio bursts, or FRBs, and in the search for gravitational waves.
Parkes also played a leading role in previous SETI searches. In 1995 the California-based SETI Institute used the telescope for six months for its Project Phoenix search. The Parkes telescope provided the critical capability to search the southern sky that could not be accessed using telescopes in the northern hemisphere.
The latest initiative is being led by a number of the world’s most eminent astrophysicists and astronomers. Professor Matthew Bailes, ARC Laureate Fellow at the Centre for Astrophysics and Supercomputing at Swinburne University of Technology in Melbourne, will be the Australian lead of the SETI observing team using the Parkes telescope.
The program will nicely complement the existing scientific uses of the Parkes telescope. Although it will take up a quarter of Parkes time, it will benefit the research undertaken during the other three-quarters of the time the telescope is in operation.
It will enable even greater scientific capability to be provided to a wide range of astronomy research through both the financial support and through the provision of new data processing and analysis systems and techniques.
Incredible advances in computing technology make it possible for this new search to scan much greater swaths of the radio spectrum than has ever before been explored. Rather than trying to guess where on the radio dial astronomers might receive a signal, they can now search an entire region of the radio spectrum in a single observation.
The dramatic increase in data processing capability has also meant that astronomers can analyse telescope data in new ways, searching for many different types of artificial signals.
CSIRO is thrilled to be part of this global initiative which takes advantage of the significant advances that have been made in computation and signal processing since the search for extraterrestrial life began.
The probability of detecting intelligent life is small but it is much greater today than ever before. To be the first to discover intelligent life would be a phenomenal achievement not only for the scientific community but for all humankind.
We’re playing a vital role in NASA’s New Horizons mission, the first ever attempt to visit Pluto. Learn more about this historic exploration, and our other astronomical feats, at #CSIROSpace.
Talk about a long distance call.
Some time tonight, around 9:57pm AEST, we’re expecting a world-first ‘phone call’ from the outer edges of the solar system.
The team at our Canberra Deep Space Communications Centre (CDSCC) will be the first to hear from the New Horizons spacecraft as it completes its nine-and-half-year journey to the solar system’s most famous dwarf planet, Pluto. NASA and Johns Hopkins University Applied Physics Laboratory are the lead agencies on this multi-million dollar project, but our CDSCC facility will be integral in communicating with the far-flung vessel.
Scientists have never before had an opportunity to study Pluto and its surrounding moons (Charon, Hydra, Nix, Styx and Kerebros) with such detail and precision. Even images from Hubble have shown us little more…
The Pluto Nine: Rubie, Jayda, Anthony, Sam, Sophie, Sudistee, Ryan, Kelan and Caitlin.
NASA has spent the last nine years navigating New Horizons towards Pluto. Within days, the first high resolution images will be beamed back to earth giving the world its first real insight into what makes the tiny ‘planet’ tick. But for now, not even NASA can claim to know very much about it. So we thought we’d speak to some of Australia’s youngest and brightest minds to see what they think.
In summary, here are five ways NASA can prepare for an encounter with Pluto.
Before you get to Pluto give them a call, and let them know you’re coming: According to our ‘young astronomers’ there is a man on Pluto with a phone, and he may be able to tell you how cool or fun it is before you get there.
Hi and bye: pulsar J2032+4127 is not going to linger near its companion. Artist’s impression: NASA
A non-standard search method has turned up a highly unusual star — a “fly-in, fly-out” pulsar that orbits its companion star just once every 25 years.
The pulsar, called J2032+4127 (or J2032 for short), is the crushed core of a massive star that exploded as a supernova. It is a magnetised ball of ‘neutron star matter’ about 20 km across, about 1.4 times the mass of the Sun, and spinning seven times a second.
It lies 5,000 light-years away, in the constellation of Cygnus (the Swan).
Many pulsars emit pulses of both radio waves and gamma rays. J2032 is one of them, and was discovered when NASA’s Fermi Space telescope spotted its varying gamma rays.
NASA’s Fermi space telescope. Image: NASA
Once they knew exactly where to look, radio astronomers too were able to detect J2032. A team at the UK’s University of Manchester kept tabs on the object from 2010 to 2014. And they noticed something odd.
There were strange variations in both the pulsar’s rotation and the rate at which the rotation was slowing down. The most likely explanation was that the pulsar is orbiting another star — and in a very large orbit.
J2032 turns out to be the longest-period binary pulsar known, and has an extremely eccentric (that is, elongated) orbit. Like a long-period comet orbiting the Sun, it swoops in from a distance, makes a quick turn around its star, and then flies off again. The pulsar and its companion have a mostly long-distance relationship, with the occasional close encounter.
The orbit of the pulsar (big ellipse) and its companion star (small ellipse) around their mutual centre of mass. The numbers around the big ellipse mark the number of days from the pulsar’s point of closest approach to its star (periastron). The darker parts of the ellipse represent the part of the pulsar’s orbit that took place while the pulsar was being timed during 2010-2014.
The companion star is called MT91 213. Classified as a Be star, it has 15 times the sun’s mass and is 10,000 times brighter. Be stars have strong outflows of material, called stellar winds, and are embedded in large disks of gas and dust.
CSIRO astronomer Dr Matthew Kerr, a member of the team that found the pulsar, contributed an improved method of pulsar timing that facilitated the discovery.
As we search for pulsars in new ways, “we’ll turn up more and more unusual ones,” Dr Kerr said. “This could change our ideas about the nature of the whole pulsar population.”
Astronomers think the supernova explosion that created the pulsar also kicked it into its eccentric orbit, nearly tearing the binary apart in the process.
When the pulsar whips close by its companion in early 2018, it will plunge through the disk of material around the Be star and trigger astrophysical fireworks, which astronomers will study with a range of telescopes.
“The pulsar will serve as a probe, letting us measure the massive star’s magnetic field, stellar wind and disk properties—something we couldn’t do any other way”, Dr Kerr said.
A study of the system, led by Professor Andrew Lyne of the University of Manchester, was published on 16 June in the journal Monthly Notices of the Royal Astronomical Society.
Australia’s key role in NASA’s New Horizons mission
Historic Encounter: Artist’s concept of the New Horizons spacecraft flying past Pluto and Charon. Image: NASA
After a voyage of 3,443 days and travelling nearly 5 billion kilometres from home, NASA’s New Horizons spacecraft is now just 20 days away from its historic encounter with the distant world of Pluto.
The science team located at the Applied Physics Laboratory (APL) at the Johns Hopkins University in Baltimore, Maryland and the Southwest Research Institute (SwRI) in San Antonio, Texas have been dreaming of this moment since plans for the mission were first hatched back in 1989.
Listening for Whispers: Canberra Deep Space Communication Complex.
In Australia, our tracking station is managed on NASA’s behalf by the CSIRO. Operated by an all Australian team of engineers, technicians and spacecraft communication experts, the station is located at Tidbinbilla just outside of Canberra.
Just like their counterparts at APL, SwRI, NASA and the Jet Propulsion Laboratory (JPL), the team at the Canberra Deep Space Communication Complex (CDSCC) are ready for the July 14 encounter with Pluto. CDSCC has been following the entire voyage of New Horizons since its launch on January 19, 2006 and are set to play a key role in the one of the most anticipated planetary encounters in space exploration history.
CDSCC has been tracking the New Horizons spacecraft since its launch in January 2006. Image: Canberra Times/Fairfax
To start its prime mission, the New Horizons spacecraft has ventured further than any other mission. It has encountered asteroids, flown past the giant planet Jupiter and braved the cold depths of space, ‘beeping’ home with weekly beacons to confirm that it was still alive and spending time in ‘computer’ hibernation for much of the journey.
Once at Pluto however, it will not have time to rest.
BUSY DAY: The New Horizons spacecraft has a lot of work to complete during its close encounter with Pluto. Image: NASA/Eyes on the Solar System
Not much larger than a grand piano, the New Horizons spacecraft does not have the fuel to slow down and go into orbit around or land on Pluto. Instead, after its nine and a half year journey, it will get less than one day close-up with Pluto, to learn everything it can about the dwarf planet and its family of five known moons.
Rocketing through the Pluto system at over 52,000 kilometres per hour, New Horizons will be using every instrument, sensor and camera it has to intensively study these unexplored worlds.
After such a long journey, the short encounter period places enormous pressure on the science team to ensure that everything goes right with the spacecraft and its instruments. It also heightens the focus of the CSIRO communications team in Canberra who will be working throughout the encounter period to ensure the spacecraft’s radio signal is received on Earth and that none of the valuable data is lost.
The radio signal from the New Horizons spacecraft is incredibly weak by the time it is received on Earth. The 12-15 watt transmission is not a tight beam. As it travels through space, the radio waves spread out, becoming thinner and more diffuse. By the time it has travelled across the 4.8 billion kilometres of void, the spacecraft’s signals – which at the speed of light have taken 4.5 hours to reach us – are received at CDSCC’s antenna dishes at signal strength of 4 x 10-19 watts (that’s 0.00000000000000000004 of a watt!) Literally, a whisper from deep space.
BIG DISH: CDSCC’s 70-metre antenna dish, Deep Space Station 43 is keeping an ‘ear’ on New Horizons.
The incredible sensitivity of CDSCC’s big dish, Deep Space Station 43 (DSS43) will be used as the prime antenna to receive these signals and collect from New Horizons some of the first close-up images of the dwarf planet.
CDSCC will also be working side-by-side with its sister stations to complete a critical science experiment at Pluto called REX (Radio science EXperiment). By transmitting a powerful radio signal towards Pluto and having it received on-board the New Horizons’ REX instrument, scientists will be able to determine more about the density and temperature range of Pluto’s tenuous atmosphere, and find out whether its largest moon, Charon also has an atmosphere.
The precise timing of the transmission will coincide with the moment the spacecraft starts passing behind the dwarf planet from Earth’s point of view. Knowing exactly when the signal is received at the spacecraft, lost when it passes behind the dwarf planet and regained again when Earth is in view, will allow scientists to increase our knowledge of the size of Pluto down to an accuracy of just a few metres.
PLUTO: Images from New Horizons’ LORRI camera are revealing intriguing features on Pluto’s surface. Image: NASA/APL/SwRI
The countdown continues, and Pluto is getting bigger in New Horizons’ cameras every day. Recent pictures received on Earth are already showing a world with wide variation of light and dark features. What these turn out to be is just a small part of the many mysteries that New Horizons hopes to answer.
What will New Horizons find? What questions will be answered and what new mysteries raised?
INTO THE DARK: New Horizons’ journey continues beyond Pluto. Stay Tuned. Image: NASA/APL/SwRI
One thing is certain, the CSIRO team at the Canberra Deep Space Communication Complex will be playing its part. Just like the mission scientists who have waited so long for this day, CDSCC is counting the days, hours minutes and seconds remaining until the time of New Horizons’ closest approach to the realm of Pluto and its moons.
Put it in your diary, the moment arrives at 9:49.57pm (AEST) on Tuesday, July 14th, 2015.
T minus 20 days and counting.
For further information: The New Horizons mission – visit its website or follow on Twitter.
See what the antennas of the Deep Space Network are doing 24/7 via DSN Now.
Follow the New Horizons Pluto encounter with Eyes on the Solar System.
PhD student Joe Callingham. Joe is co-supervised by the University of Sydney and CSIRO, and is also affiliated with CAASTRO, the ARC Centre of Excellence for All-Sky Astrophysics. Photo: CAASTRO
A galaxy that ‘died’ around the same time as England’s King Richard III may help astronomers improve their cosmic accounting.
According to PhD student Joe Callingham, this galaxy, a strong radio source called PKS B0008-421, gave up the ghost just 550 years ago — about the time the Wars of the Roses were raging in England.
In astronomical terms, that’s the blink of an eye.
The Battle of Barnet (1471), a key clash during the Wars of the Roses. Richard III was killed in 1485, at the Battle of Bosworth. (Public domain image.)
PKS B0008-421 was discovered with our Parkes radio telescope in the 1960s.
At first glance, it’s a completely boring source. Just a dot in the sky, it has doesn’t seem to have changed since it was discovered: not grown stronger or weaker, or changed shape or size.
But an unchanging source like this is actually really valuable to radio astronomers: they use it as a reference, a calibrator, to monitor the performance of their telescopes.
From time to time calibrators have to be observed in their own right, to check that they have not, in fact, changed. So there are lots of observations of PKS B0008-421, dating back to the 1960s.
Joe plotted up this historical data, plus more recent observations made with our Compact Array (which detects short radio waves) and the Murchison Widefield Array (which detects longer radio waves).
And he found something interesting.
CSIRO’s Compact Array radio telescope. (Image: D. Smyth).
PKS B0008-421 is thought to be a baby radio galaxy — small, but with an active black hole pumping out radio-emitting particles.
It has a very sharply peaked radio spectrum, and so is classified as a gigahertz peaked spectrum or GPS source.
Since the 1960s astronomers have had a model, an explanation, for how GPS sources work and the sharply peaked curve their radio spectrum follows.
But Joe found that the conventional model didn’t fit PKS B0008-421 as well as an alternative one.*
This could shake up astronomers’ ideas about the age of GPS sources and the environments they live in.
What’s more, Joe could make the models fit the data only by assuming that the galaxy’s central black hole had stopped spitting out high-energy particles about 550 years ago.
In other words, the black hole has ‘turned off’. PKS B0008-421 is now slowly dying.
Once a source like this has turned off, it will fade rapidly — unless it is cocooned in dense gas. We think PKS B0008-421 has this dense gas.
New low-frequency radio telescopes such as the Murchison Widefield Array should be able to pick out more dying, gas-swaddled sources like PKS B0008-421.
The Murchison Widefield Array. Photo: Curtin University
What does this have to do with ‘cosmic accounting’?
As we said, PKS B0008-421 is thought to be a baby radio galaxy.
If all went well, this galaxy and others like it would eventually grow into giant radio galaxies. These can be as big as a whole bunch of galaxies the size of our Milky Way.
The problem is, we can find many more babies than we can giants.
If we could find many radio galaxies that have died young, we might be able to reconcile the numbers of small, young radio galaxies and old, giant ones.
The giant radio galaxy Centaurus A, to scale on the sky. The Compact Array image of it is the most detailed ever made. I. Feain, T. Cornwell, R.D. Ekers, R. Morganti, N. Junkes. ATCA photo: S. Amy
To get a handle on what’s happening inside galaxies like PKS B0008-421 — how they make their radio waves — we need to know how dense the hydrogen gas inside them is. This problem should be licked by a survey such as FLASH, which will run on our ASKAP telescope.
Joe recently presented his work at a meeting in Italy.
An elevated view of our ASKAP antennas at the Murchison Radio-astronomy Observatory. Credit: CSIRO.
*Note for nerds: the conventional model to explain the radio emission is synchrotron self-absorption; the alternative model is free-free absorption.