25th Anniversary of SN1987a

This February marks the 25th anniversary of the discovery of Supernova 1987A.  A star, in the Tarantula Nebula within the Large Magellanic Cloud (LMC), called Sanduleak 69 202, exploded and became a supernova back on 24th February 1987.

It is now 25 years since the light from this cosmic explosion first reached us here on Earth. The star itself actually exploded about 168,000 years before, of course, with the light taking that long to reach us.

SN1987A has become the most studied star remnant in history and has provided great insights into supernovae and their remnants. It has some interesting connections to the Anglo-Australian Observatory and Siding Spring and is still being studied to this day.

SN 1987A was discovered by Ian Shelton and Oscar Duhalde at the Las Campanas Observatory in Chile on February 24, 1987, and within the same 24 hours independently by Albert Jones in New Zealand. On March 4–12, 1987 it was observed from space by Astron, the largest ultraviolet space telescope of that time. Hubble had yet to be launched.

On February 23rd, approximately three hours before the visible light from SN1987A reached the Earth, a burst of neutrinos was observed at separate neutrino observatories around the globe. This is likely due to neutrino emission (which occurs simultaneously with core collapse) preceding the emission of visible light (which occurs only after the shock wave reaches the stellar surface).

At 7:35 a.m. Universal time, Kamiokande II detected 11 antineutrinos, IMB 8 antineutrinos and Baksan 5 antineutrinos, in a burst lasting less than 13 seconds. Even though, the actual neutrino count was only 24, this was a significant rise from the previously-observed background level. This was the first time neutrinos emitted from a supernova had been observed directly, and marked the beginning of what is now ‘neutrino astronomy’.

The Supernova exploded in the Tarantula Nebula area near the edge of the Large Magellan Cloud – a satellite galaxy to our own. Even though its location in the LMC meant it was 10 times more distant than if it had been in our own Milky Way, it also meant that we had a relatively unobscured view of the supernova and its environment; there was never any ambiguity about its distance; and the fact that it lies so far south meant that observations could be done each night throughout the first year as it was always visible at some time during the night.

SN1987A was the brightest and closest supernova that has been seen since the invention of the telescope back in 1604. That supernova was called “Kepler’s Star” and the supernova was in our own galaxy around 20,000 light years away. It was so bright that it outshone Venus and Jupiter and was even visible in daylight for 3 weeks back then. The only other one in our own galaxy was “Tycho’s Star” seen in 1572 and also visible to the naked eye. There have only been a total of 8 naked eye supernova that are known.

SN1987 was also It was able to be seen quite easily with the naked eye, despite not even being in our own Milky Way galaxy. Visible for some months afterwards, it was easy to find and exciting to point out to others this bright new star in the LMC. 

SN1987A provided some significant opportunities  specific to the decade that followed and which came about as a direct result of the supernova discovery. These include the development of infrared instrumentation and spectropolarimetry which were evolving rapidly at the AAT and elsewhere. At the time of the supernova, photographic film was still in use at observatories and the internet did not yet exist. All discovery communications were done by telex between the various observatories around the world.

Data was shipped on large tapes back across to England and the other observatories to be reduced and analysed.

Even the introduction of CCDs, with their great sensitivity and dynamic range, made a major difference during the first few years. But much more importantly, the Hubble Space Telescope became available not long after the explosion.  We would have learned a lot less about SN1987A had it occurred a decade earlier, and there is unfortunately no guarantee that we will have any HST-like capability even 10 years from now.

Pioneer Astrophotographer,  David Malin, was working at the Anglo-Australian Telescope at the time of SN 1987A’s first sighting and was able to take several images of the light echoes of the supernova. One of his images is shown below.

Although the AAT observing schedule had been fully assigned for the semester through to June , when SN1987A erupted, data was able to be obtained on almost two thirds of the nights, and those observations took up 16% of the total time available. This was achieved by using up all the engineering, service and director’s time, as well as, requiring each observer to give up one hour per night of their time to allow observations with whatever instrument was on the telescope. The observers willingly co-operated and so much incredible data was able to be collected.

The emphasis was on observations that could best utilise the 3.9m aperture of the AAT or observations which best used the available instrumentation unique to that telescope: for example, speckle interferometry and spectro-polarimetry.

The Anglo-Australian Telescope was ideally situated as it was the only telescope from which the supernova was accessible and which had the necessary instrumentation to make the observations. Even though there were some changes necessary to the existing IPCs based spectro-polarimeter which was optimised for observing much fainter object.

 Data was collected by the non-optimised instrument 4 days after the discovery and it was found that the instrument issues meant that data accuracy would be impacted. So over the next 10 days the engineers worked to modify the instrument to use CCDs as detectors and the first observations with were made on March 7th, a mere 2 weeks after the supernova was first seen.

One particular highlight was the very rapid construction, by Peter Gillingham, of a temporary Littrow spectrograph, which had a resolving power of almost one million, which  was able to be used to study interstellar lines. It was available within 2 months of the Supernova. It has been called the  “wooden spectrograph”.

The new CCD spectropolarimeter – was built up from the RGO spectrograph  plus Pockels cell plus IPCS which itself was a well proven set-up. In order to make it all work with incredibly bright object – the instrument was modified to use the CCD detectors. This raised further hurdles which were one by one overcome and they were able to collect over the next 12 months the first ever spectropolarimetry data on a supernova.

A common-user version of this very successful Ultra-High Resolution  Spectrograph  (UHRF) was later  commissioned and operates on the telescope to this day. Peter Gillingham was able to very quickly come up with a temporary version of a coude mounted spectrograph by combining a novel Littrow lens design with one of the gratings that was eventually destined for use on the UCLES instrument. It was the success of this project which meant they were able to obtain funds to later build the new instrument.  The original instrument was first housed in a large wooden box.

 The AAT was perfectly placed geographically and so was able to get onto observing this supernova very quickly. It has now been observed for many years and the campaign in radio, infra-red and optical continue to this day since 25 years is a long time to us – but rather infinitesimal in the scale of the universe.

So was it just luck? Being in the right place at the right time?

Personally, I don’t think so – I think it was having this amazing instrument up here at Siding Spring and a really innovative group of staff who were able to think outside the box and design instruments and obtain data on this incredible supernova explosion in a very short space of time. Luck may have been the SN going off nearby – but skill and dedication was what made all the difference.

 

SN1987a before and after by David Malin Anglo-Australian Telescope - used with permission

This photograph shows the field around the site of the supernova in great detail, both before the supernova exploded (right) and about 10 days afterwards, when it was still brightening. The image of the star that exploded to create the supernova is elongated. This does not necessarily indicate any peculiarity or a close companion, rather it is the effect of stars being by chance aligned along the line of sight. Several other examples can be seen in this picture and other, different, blended images are seen in the photograph of the same field taken two weeks after the supernova appeared (left). The pre-supernova plates were taken over about 90 minutes on the night of 1984 February 5, centred on the Tarantula nebula. The post-supernova plates (LHS image) were exposed for a total of about an hour on the night of 1987 March 8.

 The difference in image quality (‘seeing’) between these pictures is an effect of the Earth’s atmosphere which was much steadier when the plates used to make the pre-supernova picture were taken. Top left is NE. Width of each image is about 8 arc minutes. Text and Image © 1989-2010, Australian Astronomical Observatory, photograph by David Malin.

 

 

Planetary Alignments in the Evening Sky

Over the next 4 weeks, the solar system’s brightest planets will be putting on a spectacular evening show as they start to move into formation over the nights to come.

If you go out just after sunset and look towards the west, you will see Venus and Jupiter popping out of the twilight even before the sky has gone completely dark. After you have found them once or twice you will be able to find them earlier.   Seeing these two brilliant planets surrounded by darkening blue of the evening sky is a lovely sight.

If you go out at the next night, the view improves, because Venus and Jupiter are converging.  In mid-February they were about 20 degrees apart but by the end of the month, the angle narrows to only 10 degrees—so close that you can hide them together behind your outstretched palm.  Their combined beauty grows each night as the distance between them shrinks.

 A special night to look is Saturday, February 25th, when the crescent Moon moves in to form a slender heavenly triangle with Venus, Jupiter and the Moon as its vertices.  One night later, on Sunday, February 26th, it happens again.  This arrangement will be visible all around the world, from city and countryside alike.  The Moon, Venus and Jupiter are the brightest objects in the night sky; together they can shine through city lights, fog, and even some clouds.

 After hopping from Venus to Jupiter in late February, the Moon exits stage left, but the show is far from over.

 In March, Venus and Jupiter continue their relentless convergence until, on March 12th and 13th, the duo lie only three degrees apart—a spectacular double beacon in the sunset sky. Now you’ll be able to hide them together behind a pair of outstretched fingertips.

 There’s something mesmerizing about stars and planets bunched together in this way. This strange phenomenon is due to the fact that your eye works in much the same way as a digital camera does. In front, there is a lens which focuses the light and the retina acts like a photo-array behind the lens to capture the image of what you see. The retina is made up of rods and cones which are the organic equivalent of electronic pixels.

 There’s a tiny patch of tissue near the centre of the retina where cones are extra-densely packed. This is called “the fovea.” This enables you to see objects in high definition – it is critical to everyday tasks such as reading, driving and watching television. The fovea has the brain’s attention.

 The field of view of the fovea is only about five degrees wide. Most nights in March, Venus and Jupiter will fit within that narrow cone.  And when they do—presto!  It’s spellbinding astronomy.

Mission to Land on a Comet

Europe’s Rosetta spacecraft is en route to intercept a comet– and to make history. In 2014, Rosetta will enter orbit around comet 67P/Churyumov-Gerasimenkoand land a probe on it, two firsts.

 Rosetta’s goal is to learn the primordial story a comet tells as it gloriously falls to pieces. Comets are primitive leftovers from our solar system’s ‘construction’ about 4.5 billion years ago. Because they spend much of their time in the deep freeze of the outer solar system, comets are well preserved—a gold mine for astronomers who want to know what conditions were like back “in the beginning.”

 As their elongated orbits swing them closer to the sun, comets transform into the most breathtaking bodies in the night sky. A European Space Agency mission launched in 2004 with U.S. instruments on board, Rosetta will have a front-row seat for the metamorphosis.

 At the moment, Rosetta is “resting up” for the challenges ahead. It’s hibernating, engaged in its high-speed chase while fast asleep.

It will be woken up on or around New Year’s Day 2014, to begin a months-long program of self-checkups.

 If all goes well, in August that year, Rosetta will enter orbit around 67P’s nucleus and begin scanning its surface for a landing site. Once a site is chosen, the spacecraft will descend as low as 1 km to deploy the lander.

 The lander’s name is “Philae” after an island in the Nile, the site of an obelisk that helped decipher—you guessed it—the Rosetta Stone.  Touchdown is scheduled for November 2014, whenPhilaewill make the first ever controlled landing on a comet’s nucleus. Because a comet has little gravity, the lander will anchor itself with harpoons.

 Once it is fastened, the lander will commence an unprecedented first-hand study of a comet’s nucleus. 

 Meanwhile, orbiting overhead, the Rosetta spacecraft will be busy, too. On board sensors will map the comet’s surface and magnetic field, monitor the comet’s erupting jets and geysers, measure outflow rates, and much more.  Together, the orbiter and lander will build up the first 3D picture of the layers and pockets under the surface of a comet.

Venus and the Crescent Moon

Venus presents a nice photo opportunity later this month. Venus can be clearly seen in the late twilight this month as the very, very bright and beautiful “Evening Star” in the Western Sky after Sunset. Venus appears as a distinct “half Moon” shape in even small telescopes. On February 25 Venus and the Crescent Moon are close together with Jupiter not far away. With a nice foreground – this could be a make a very nice photograph.

Check out Venus, the crescent Moon and Jupiter tonight! Western Sky just after sunset

 

Stuck in the Sky – the ISS Crew return to Earth Delayed.

The International Space Station crew will spend some 45 extra days in orbit after a space flight schedule was shifted. The next launch had to be delayed after a Soyuz capsule failed factory tests.

The replacement for the ISS crew will now not travel to the station until mid-May, the head of the unmanned space exploration department at Roscosmos said on Thursday.

 

The current expedition was started two months later than scheduled to allow extra safety tests to be carried out following the crash of a Progress freighter last August. Therefore the extra 45 days in orbit will simply make the mission roughly the same length as a number of previous ones.

 The decision to delay the next Soyuz launch was taken together with NASA and other partners in the ISS program, the Russian official said. It came after the return capsule of the Soyuz-TMA-04M failed a factory test. The capsule cracked during an airtightness test, making it unfit for a space flight, a source told Interfax news agency.

The failure was either due to a manufacturing defect or excessive pressure applied during the test. An investigation into the cause of the setback is currently underway.

Roscosmos decided to use the Soyuz-TMA-05M in the place of the failed vehicle. The spacecraft was renamed 04M accordingly.

 A launch date for the new Soyuz-TMA-05M, the successor to the new Soyuz-TMA-04M, has yet to be set, Krasnov said. It will follow the launch of a Japanese HTV freighter and is expected in mid-July.

 The initial plan was to use undamaged parts of the spacecraft and the descent capsule from another one. But engineers decided it would be too risky and time consuming, because the 05M’s design was slightly altered as compared to the 04M, industry insiders said.