Astronomy & Space June 2016 by Richard S Pearson

In Search of the first stars Presented by Richard Pearson

Astronomy & Space.tv is an educational program for amateur astronomers, and students, worldwide. It has been produced and presented monthly in its current format since December 2013 by Richard Pearson who is a former journalist and science correspondent. The show first aired as a tribute to the later Sir Patrick Moore who popularised astronomy for over 55 years in the BBC Sky at Night program, who sadly died in December 2012. Astronomy & Space enjoys a monthly audience of about 100,000 viewers world-wide, and all the previous shows are available to see again for FREE on our Vimeo channel, and can be found on our website at http://astronspacetv.blogspot.co.uk/ If you like this program, please share it with your friends, and members of your local astronomical society.

ASTRONOMY & SPACE JUNE 2016: SEARCHING FOR THE FIRST STARS Two of these galaxies are the most distant of their kind, so distant that their light began its journey when the Universe was only one billion years old. Even more interesting, in one of the galaxies, water is among the molecules detected, marking the most distant observations of water in the cosmos to date.

In this month’s program we are going to be looking at the first stars & galaxies that formed in the universe soon after what astronomers call the big bang.

A few days ago Professor Marusa Bradac and her team published a paper about their newest find. They have now broken her own record to discover a new galaxy in the early universe that is just 13 billion years old.

The most intense bursts of star birth are thought to have occurred in the early Universe, in massive, bright galaxies. These starburst galaxies convert vast reservoirs of cosmic gas and dust into new stars at a furious pace — many hundreds of times faster than in grand spiral galaxies like our own galaxy, the Milky Way. By looking far into space, at galaxies so distant that their light has taken many billions of years to reach us, astronomers can observe this busy period in the Universe’s infancy.

In March 2013 an international team of astronomers led by Marusa Bradac, a professor at University of California first discovered these distant and enigmatic starburst galaxies with the US National Science Foundation’s 10-metre South Pole Telescope (SPT). A radio telescope built in 2007 at the Amundsen–Scott South Pole Station, at Antarctica.

Marusa and her team made the discovery using an advanced spectroscope fitted on the ten-meter Keck II telescope, at the William Keck Observatory on the summit of Maunakea, in Hawaii. It was made possible through a phenomenon predicted by Einstein in which an object is magnified by the gravity of another object that is between it and the observer; astronomers call this a gravitational lens. In this case, the detected galaxy behind the galaxy cluster was MACS 2129, which is massive enough to create three different images of the object.

Then Prof Marusa Bradec used the Atacama Large Millimeter/submillimeter Array in Chile to zoom in on them to explore the formation of the first stars in the young Universe. The team was surprised to find that many of these distant dusty star-forming galaxies are even further away than expected. This means that, on average, their bursts of star formation took place 12 billion years ago, when the Universe was just under 1.7 billion years old — a full billion years earlier than previously thought.

This new discovery is quite remarkable, if only because there are merely two women astronomers lead this splendid field of research today, Professor Marusa Bradac, and Professor Anna Frebel shown here. Anna works in the

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ASTRONOMY & SPACE JUNE 2016: SEARCHING FOR THE FIRST STARS Department of Physics at the Massachusetts Institute of Technology.

will give clues that will help us to understand how these objects form and evolve.

Our universe came into being 13.7 billion years ago in what has become known as the Big Bang. We can never look back to see the moment of creation in any one direction, because we are in the middle of it, and the remnants of the Big bang are all around us.

The James Webb telescope now under construction is the next generation space observatory. It has a 6½ meter mirror that will provide remarkable sensitivity from longwavelength (orange-red) visible light, through near-infrared to the mid-infrared, and is the successor instrument to the Hubble Space Telescope and the Spitzer Space Telescope. A large sunshield will keep its mirror and four science instruments below −220 °Centigrade.

Would that make the Universe 27.4 Billion light years across? – No, after the initial inflation period the Universe has continued to expand. So, a galaxy which sent its light 13 billion light years away is now over 40 billion light years distant from us. The so-called observable Universe is over 92 billion light years in diameter, however, we have no idea what lies beyond. To be able to observe the Cosmos after the moments of creation we are going to need a really big telescope, and to see through the dust and gas hiding it from view, it will also need special infrared vision.

One special study with the telescope involves observing some of the most distant objects in the Universe, beyond the reach of existing ground and space-based instruments. This includes the very first stars, during the age of what astronomers call ‘Reionisation’, and the formation of the first galaxies. Another goal is to understand the formation of stars and planets. This will include imaging molecular clouds and star-forming clusters.

Our Earth is an exceptional planet that is teaming with life, and is home to us humans. We are fortunate to be orbiting around a steady star, the Sun, in a relatively warm habitable region of the solar system that enables life to flourish.

In Chile, astronomers at the European Southern Observatory, affectionately known as ESO, are busy constructing the Extremely Large telescope, or ELT. Its 40-meter mirror and adaptive optics will provide clues to understanding the formation of the first objects that formed: primordial stars, galaxies, black holes and their relationships. The ELT is designed to make detailed studies of the first galaxies and to follow their evolution through cosmic time. Observations of these early galaxies

As Professor Carl Sagan reminded us so many times, we are all made of star stuff cooked up inside the first stars. The requirements for the existence of life were all met by the time our Sun formed. Our Sun is a second generation star whose birth nebula formed by the supernova explosion of the first stars to form in the Universe less than half a million years after the Big Bang. Finding and studying these first stars is a new branch of astronomy that will help us better understand the Universe around us.

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ASTRONOMY & SPACE JUNE 2016: SEARCHING FOR THE FIRST STARS Our galaxy, the Milky Way, is a huge island of 400 billion stars laid out in the form of a spiral. Its size is so huge that travelling at the speed of light it would take a space traveller 150,000 years to trek across the galaxy from one side to the other, which is a very recent estimate. I made a program about this in May 2015 called Galactic whirlpools.

Then in 2015 a team of astronomers led by David Sobral, from the Faculty of Sciences of the University of Lisbon in Portugal, and the Leiden Observatory in the Netherlands, used ESOâ&#x20AC;&#x2122;s Very Large Telescope to look back into the ancient Universe, to a period known as Reionisation, about 800 million years after the Big Bang. Their observations were also made using the William Keck Observatory and the Subaru Telescope as well as the Hubble Space Telescope. The team discovered a number of surprisingly bright very young starburst galaxies. One of these, labelled CR7, was an exceptionally rare object, and by far the brightest galaxy ever observed at this stage in the Universe. With the discovery of CR7 and other bright galaxies, the study was already a success, but further inspection provided more excitement.

The Milky Way is about 2,000 light years in thickness, and our Sun and planets lie at a safe distance of 26,000 light years from the galactic centre. The stars in our galaxy fall into two groups. Population I, or metal-rich stars, are young stars with the highest metal content in their composition. Our Sun is an example of a metal-rich star. Population II, or metal-poor stars, are those with relatively little metal. These stars formed during an earlier time of the universe. Intermediate population I stars are common in the bulge near the centre of our galaxy, whereas population II stars are found in the galactic outer regions of the galaxy, the galactic halo, which are older and more metal-poor. Globular clusters around our Milky Way contain high numbers of population II stars. Astronomers have long theorised the existence of a first generation of stars known as Population III that were born out of the primordial material from the Big Bang. All the heavier chemical elements, such as oxygen, nitrogen, carbon and iron, which are essential to life, were forged in the centres of stars. This means that the first stars must have formed out of the only elements to exist prior to todayâ&#x20AC;&#x2122;s stars: hydrogen, helium and small amounts of lithium. These Population III stars would have been enormous, several hundred or even a thousand times more massive than the Sun, blazing hot, and exploding as supernovae after only two million years. Until recently the search for physical proof of their existence had been uncertain.

Inside atoms Ionisation is the addition or removal of an electron to create an ION. Losing an electron creates a POSITIVE ION. Gaining an electron creates a NEGATIVE ION. Electrons can be lost because IONISING RADIATION forces the electron away from the atom. The astronomers found strong ionised helium emission lines in the spectra of CR7 but no sign of any heavier elements in a bright nebula in the galaxy. This meant David Sobral had discovered the first good evidence for clusters of Population III stars that had ionised gas within a galaxy in the early Universe. Within CR7, bluer and somewhat redder clusters of stars were found, indicating that the formation of Population III stars had occurred in waves as had been predicted. What the team directly observed was the last wave of Population III stars, suggesting that such stars should be easier to find than previously thought. They live amongst regular stars, in brighter starburst galaxies, not just in the earliest, smallest, and dimmest galaxies, which are so faint as to be extremely difficult to study.

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ASTRONOMY & SPACE JUNE 2016: SEARCHING FOR THE FIRST STARS The discovery of the bright cluster of young galaxies, including CR7, was a break though in the hunt for the first stars to form in the Universe. In May 2016 Astronomers at Indiana University announced that they had found a faint blue galaxy nicknamed Leoncino, or "little lion," which contains the lowest level of heavy chemical elements, or "metals," ever observed in a gravitationally bound system of stars.

Officially, the "little lion" is named AGC 198691. It is about 30 million light-years from Earth and lies in the constellation Leo Minor (the lion cub). Alec Hirschauer and his team obtained spectra of the single emission nebula region in Leocino with the 4Â˝ m Multiple Mirror Telescope on Mt Hopkins at Arizona in the US. These observations enabled the measurement of the temperaturesensitive Oxygen-iii line, and therefore they were able to observe the "direct" oxygen abundance for Leoncino. The astronomers found this system to be an extremely metal-deficient with an oxygen richness of 7, making Leoncino the lowest-abundant starforming galaxy known in the local universe to date. Apart from low levels of heavier elements, Leoncino is unique in several other ways. A socalled "dwarf galaxy," it is only about 1,000 light years in diameter and composed of several million stars. The Milky Way, by comparison, contains up to 400 billion stars. The conditions in the early universe following the Big Bang were beyond our understanding. Nothing existed before the Big Bang, and time only came

into existence at the same moment our universe formed. What we know, is that immediately after the Big Bang the Universe was extremely hot and consisted of a thick soup of various kinds of tiny atomic particles. During the minutes that followed, protons, neutrons, and electrons, the building blocks of atoms, formed. The Universe then expanded quickly cooling in the process. The only chemical element that existed up to that point had been hydrogen in the form of protons. After two to three minutes the temperature had cooled to one billion degrees.

The first elements heavier than hydrogen, including deuterium, were formed. Deuterium is also called "heavy hydrogen" because it has the same atomic number as hydrogen, except it is composed of one proton and one neutron. From deuterium, the first helium element formed. The collisions of several helium atoms caused the third heaviest element, lithium, to occasionally form in small amounts. The Universe was then composed of three elements: hydrogen, helium, and lithium. Roughly 75% of the total mass consisted of hydrogen, 25% helium, and a tiny fraction of lithium. The first phase of element making was complete just three minutes after the Big Bang. For life to later evolve in the Universe and for humans to emerge, these three chemical elements were not enough. The elements needed to sustain life, including carbon, nitrogen, oxygen, and other elements in the periodic table, were still missing. Those were later built up inside stars over billions of years. Only the interiors of stars are hot enough for heavier elements to be successively made from the available lighter elements, such as hydrogen and helium.

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ASTRONOMY & SPACE JUNE 2016: SEARCHING FOR THE FIRST STARS These stars, and later also galaxies, had to emerge first. For that, the first atomic particles had to combine with the free electrons in the Universe to form neutral atoms. For quite some time after the Big Bang, these atoms were racing about in a cosmic jumble, and the energy and direction of the photons were constantly being scattered. So this soup of particles and rays was fairly opaque, resembling a thick fog. About 380,000 years after the Big Bang, the Universe had grown so much while cooling down that a fundamental change occurred when it reached about 2,700° C. The nuclei and electrons were moving slowly enough by then that the positively charged nuclei could capture the negatively charged electrons to bind them together. The photons that had been flying around since the Big Bang suddenly had much less chance of being scattered, and the universe became transparent for the first time. At last, the photons were liberated from the electrons and could travel long distances unrestricted. Today we call this ‘The Cosmic Background Radiation’. This is the faint left over glow of the Big Bang from almost 13.7 billion years ago.

Since becoming transparent, the Universe has grown over a 1000 times larger. The energy density of the cosmic background radiation decreased as the Universes volume increased. For that reason, the temperature of the background radiation reaching us today is not 3,000°C but only -270° C. As it continues to expand, someday in the very far future it will reach absolute zero. A few hundred million years passed before the Universe completely changed its qualities yet again. The "dark ages" that had persisted since the atomic nuclei had begun capturing electrons came to an end. The first stars in the Universe emerged from the giant and increasingly clumpy clouds of gas. They were composed of just the hydrogen,

helium, and lithium of the primordial soup left behind after the Big Bang. In this way the Universe was lit up for the very first time. The Ultra Violet light emitted by these stars led to the ionization of neutral atoms in the gas clouds. The intense stellar radiation had dislodged the electrons from their atoms. As I said previously, in atoms Ionisation is the addition or removal of an electron to create an ION. Electrons can be lost because IONISING RADIATION forces the electron away from the atom. The very existence of the first stars had therefore altered the conditions for the formation of later stars like our Sun. As a result, star formation continued more efficiently and greater numbers of stars formed, and, together with the gas, they arranged themselves in huge clouds of stars known as galaxies. In their hot interiors, the first stars made chemical elements heavier than hydrogen and helium. This production of additional elements led to big changes in the Universe. From that time on, countless stars began to chemically enrich the surrounding gas in their galaxies. After about nine billion years, enough of the elements had collected for the formation of our Sun and the solar system. At present, after 13.7 billion years of cosmic evolution, the mass fraction of the elements from lithium to uranium is about 2%. When the Sun was born 4½ billion years ago, it was about 1½ %. Apart from any lithium, all this material was produced inside stars. For this reason, the oldest ones are the key to understanding exactly how the chemical mixture now present in the Universe developed over time. A stroke of good fortunate came in the spring of 2015 when a team of astronomers, led by Darach Watson from the University of Copenhagen, used ESO’s Very Large Telescope, along with the radio telescope array ALMA, to observe one of the youngest and most remote galaxies ever found. The astronomers were surprised to discover a far more evolved system than expected. It had a fraction of dust of a very mature galaxy such as the Milky Way. This dust is vital for life to evolve because it helps form planets, complex molecules and normal stars.

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ASTRONOMY & SPACE JUNE 2016: SEARCHING FOR THE FIRST STARS The target of their observations is called A1689zD1 which lies in the Virgo cluster of galaxies. It is observable because its brightness is being amplified more than nine times by a gravitational lens in the form of the spectacular galaxy cluster, Abell 1689, which lies between the young galaxy and the Earth. Without the gravitational lens boost, the glow from this very faint galaxy would have been too weak to detect.

gas ratio that was similar to that of much more mature galaxies. The findings suggest A1689 is a starburst galaxy that has been consistently forming stars at a moderate rate since 560 million years after the Big Bang, or to have passed through its period of extreme starburst very rapidly before entering a diminishing state of star formation. This dusty galaxy seems to have been in a rush to make its first generations of stars. Before this result, there had been concerns among astronomers that such distant galaxies would not be detectable in this way, but A1689 was detected using only short observations with ALMA at the European Southern Observatory in Chile. Lithium-rich giant stars have also been observed in different environments: open clusters, globular clusters, the Galactic bulge, as well as in dwarf galaxies.

We are seeing A1689 when the Universe was only 700 million years old, five percent of its present age. It is a relatively modest system, much less massive and luminous than many other objects that have been studied before at this stage in the early Universe.

Recently an international team of astronomers led by Rodolfo Smiljanic of the Nicolaus Copernicus Astronomical Center in Toru, Poland, detected two giant lithium-abundant stars in an old open cluster named Trumpler 20. It lies in the constellation of Crux (the Southern Cross).

A1689 is being observed as it was during the period of Reionisation, when the earliest stars brought with them a cosmic dawn, revealing for the first time an immense and transparent Universe and ending the extended calm of the Dark Ages. Astronomers had expected it to look like a newly formed system; the galaxy surprised the observers with its rich chemical complexity and abundance of interstellar dust, yet it was a cosmic infant. At this age it would be expected to display a lack of heavier chemical elements, anything heavier than hydrogen and helium, are defined in astronomy as metals. These are produced in the centres of stars, and scattered far and wide once the stars explode as supernova. This process needs to be repeated for many stellar generations to produce a large abundance of the heavier elements such as carbon, oxygen and nitrogen.

The new stars, designated MG 340 and MG 591, were detected during an analysis of a sample of 40 giant stars of the 1.6 billion-year-old Trumpler 20 open cluster, for which high-resolution spectra were obtained using the Very Large Telescope in Chile. The astronomers estimated the mass of these stars to be between 1Â˝ and 3Â˝ times that of the sun.

Surprisingly, the galaxy A1689 seemed to be emitting a lot of radiation in the far infrared, indicating that it had already produced many of its stars and large quantities of metals, and revealed that it not only contained dust, but had a dust-to-

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ASTRONOMY & SPACE JUNE 2016: SEARCHING FOR THE FIRST STARS

We next come to Professor Anna Frebel who is a German astronomer born in Berlin in 1980. She has been working on discovering the oldest stars in the universe for over a decade. Anna is credited with the discovery of a star named HE 1327-2326 in 2003. This star shines at Magnitude +13.5 and lies in the constellation of Hydra (the water serpent). It is at least 4,000 light years away from us.

This graphic by Peter Palm shows a portion of the high-resolution spectrum of HE 1327 compared to that of a similar but more metal-rich star named G 64-12. Various absorption lines around the calcium K line are marked. In this region in HE 1327, molecular carbon (CH) lines have appeared instead of iron. Until early 2013, the record set by HE 1327 had not been broken. Then thanks to their ongoing survey work using the SkyMapper Telescope at the Siding Spring Observatory in Australia, a new amazing star named SM 0313-6708 was discovered. It was selected from the survey of 60 million stars; the candidate looked promising after a mediumresolution spectrum had been taken with the 2.3 m SkyMapper telescope.

Anna and her team could only detect four iron lines in the whole of the starâ&#x20AC;&#x2122;s spectrum. Because of its enormous iron deficiency, the star has almost no iron in it at all. The fairly warm surface temperature further reduced the strength of the lines, yet Anna found the iron abundance to be just 1/250,000th of the iron abundance in our Sun. It was hard to believe, yet Anna had found this new record holder for the most iron-poor star during the first year of her doctoral research work. The star has a carbon abundance of roughly onetenth that of our Sun, and it is not known how these two abundances can be produced together. The star was probably formed during an age of the universe when the metal content was much lower. It has been suggested that this star is part of the second generation, born out of the gas clouds which were polluted by the primordial Population III stars in the early universe.

There was no noticeable calcium line in its spectrum, making it an exciting target for highresolution spectroscopy with the Magellan Telescope in Hawaii. Soon after a spectrum could be obtained, Anna Frebel was one of the first to inspect the new data, and it turned out to be another record-breaking star. Shining at magnitude +14.7 SM 0313 lies in the southern constellation of Hydrus, and is even more remote from us at 6,000 light years. Analysis shows an upper limit on the iron abundance of less than -7 which meant that Anna had lost her record with HE 1327, to a better discovery. Anna and her team could announce that this star was one of the first stars to have formed from a gas cloud en-riched by just one single first supernova. Since 2003 several stars with about th 1/70,000 of the Sunâ&#x20AC;&#x2122;s iron abundance have been discovered. The first stars in our Milky Way processed the heavier elements, including iron, inside their cores. Because they were so huge they used up their fuel quickly and exploded as supernova, seeding the galaxy with colourful supernova remnants that we

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ASTRONOMY & SPACE JUNE 2016: SEARCHING FOR THE FIRST STARS see as nebulae. It was out of one of these stellar nurseries 4½ billion years ago that our Sun formed.

The new generation of telescopes will help astronomers better understand the formation of the very first stars and galaxies, and the evolution of the Universe. First up in 2018 will be the James Webb telescope. It will be launched into orbit on an Ariane 5 rocket from the European Spaceport near Kourou, French Guiana.

That brings this month’s program to a close, thank you for watching. Please subscribe to us on Vimeo or our website ‘Astronomy & Space BlogSpot’ so you never miss a program, and do visit our website where you can see all of our past shows. And if you like this program, please share it with your friends, and members of your local astronomical society. Until we come back next month; Good evening. Richard Pearson Email |Rpearson46@yahoo.com Website | http://astronspacetv.blogspot.co.uk/ Twitter | Richard Pearson@AstronSpace Face Book |https://www.facebook.com/richard.pearson54

The telescope’s four instruments, cameras and spectrometers, have detectors that are able to record extremely faint signals. One instrument (NIRSpec) has programmable micro shutters, which enable observation up to 100 objects simultaneously.

In our next program in July 2016 we will be looking at: ‘The Earth in Space.’

Together with the ELT in Chile astronomers, will be better equipped to understand the origin of the Universe far better than ever before, so there will be more exciting discoveries to come. © Richard Pearson July 2016: All rights reserved, no part of this publication can be re-used, or published in any form whatsoever without the written consent of Richard Pearson, and Astro-Productions. All images are the © of the owners concerned and must not be reproduced without their written consent. Full credits for the use of these images are given at the end of this month’s program.

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THE NIGHT SKY JUNE 2016 01 JUNE MIDNIGHT | 15 JUNE 11PM | 01 JULY 10PM

THE PLANETS JUNE 2016

Telescopic view of the planets this month (south pole uppermost). Times are given in UT for Birmingham (UK): (1° 54' 0" W, 52° 29' 0" N, zone Z). Date Hour Description of the phenomenon yyyy mm dd hh:mm 2016 06 01 2016 06 03 2016 06 03 2016 06 05 2016 06 05 2016 06 06 2016 06 07 2016 06 09 2016 06 09 2016 06 09 2016 06 11 2016 06 12 2016 06 12 2016 06 15 2016 06 15 2016 06 15 2016 06 15 2016 06 17 2016 06 19 2016 06 19 2016 06 20 2016 06 20 2016 06 21 2016 06 21 2016 06 26 2016 06 27 2016 06 30

00:11 06:38 10:55 02:59 12:00 21:49 02:56 22:38 23:21 23:45 13:18 08:10 20:34 01:02 11:59 22:16 23:35 02:32 01:23 11:46 11:02 22:34 21:55 23:02 23:42 18:19 01:26

Maximum of the variable star delta Cephei OPPOSITION of Saturn with the Sun Moon at perigee (geocentric dist. = 361140 km) NEW MOON GREATEST WESTERN ELONGATION of Mercury (23.9°) SUPERIOR CONJUNCTION of Venus with the Sun (geoc. dist. center to center = 0.0°) Minimum of the variable star Algol (beta Persei) Beginning of occultation of 5-xi Leo (magn. = 4.99) End of occultation of 5-xi Leo (magn. = 4.99) Minimum of the variable star Algol (beta Persei) Opposition of the asteroid 8 Flora with the Sun (dist. to the Sun = 2.419 AU; magn. = 9.4) FIRST QUARTER OF THE MOON Minimum of the variable star Algol (beta Persei) Close encounter between the Moon and Spica (topocentric dist. center to center = 4.3°) Moon at apogee (geocentric dist. = 405024 km) Beginning of occultation of 98-kappa Vir (magn. = 4.18) End of occultation of 98-kappa Vir (magn. = 4.18) Maximum of the variable star delta Cephei Close encounter between the Moon and Saturn (topocentric dist. center to center = 2.4°) Close encounter between Mercury and Aldebaran (topocentric dist. center to center = 3.8°) FULL MOON SUMMER SOLSTICE Beginning of occultation of 43 Sgr (magn. = 4.88) End of occultation of 43 Sgr (magn. = 4.88) Meteor shower : June Bootids (duration = 11.0 days) LAST QUARTER OF THE MOON Minimum of the variable star Algol (beta Persei)

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