Saturday, November 25, 2017

New Topic in Frontiers: Women in Science!!!

From 'You, me and the dancing black holes' by Edward & David


Frontiers has launched a special topic to attract women in science to publish in its pages. 


The requirement is that either the lead author is a woman or the corresponding author. Articles that appear in this topic are free of charge. I am one of the editors and I wholeheartedly support the idea of promoting science done by women. In the academic community we lose talent too easily in both genders and lose opportunities for progress because of vast bureaucracy. I strongly believe we have reached a point where we cannot afford to let go of our best people if we want humanity to survive and continue to thrive. 

From 'You, me and the dancing black holes' by  Edward & David
Women are a minority in physics, chemistry, astronomy and computer science. I have witnessed physics at top institutions, and it is unfortunately still 'a boys club', where graduate students and postdocs are almost invisible even though they do most of the work and have preciously few rights. There is also no support for the families of graduate students and postdoctoral scholars. Little miracles have to happen in each individual case to make things work. My contract ended when I was eight month pregnant with my second son. As an immigrant, I could have chosen to extend my visa for three months to look for other work -- while 8 months pregnant -- and pay the living costs for myself and three children (I also have a foster son) from my savings or move back with my parents. I chose the latter. My advisor/department said that they cannot cover maternity for a contract that would have ended on that date anyhow. When I contacted Human Resources (HR), I have been told that they might have been able to work something out for my case if I had contacted them at an earlier stage, but that departments are under no obligations to report the pregnancies of their employees to HR. I was the second unreported pregnancy in my office and the first woman to use that office space. 

Most of my colleagues who have children and PhDs have stories that are hard to hear.  The Frontiers topic is, however, not focusing on hardships, but aims to celebrate the work done by talented scientists who happen to be women and are leaders in their field or are likely to become leaders in the years to come.

Why I enjoy publishing in Frontiers?

1) It's a more modern journal that opens an interactive forum with the referees, which is less intimidating and more prone towards constructive communication. After the review process the name of the referees are made public unless explicitly requested otherwise.

2) Its rules include that articles can only be rejected based on scientific arguments and not on personal opinions of the form 'this paper is not interesting enough. so, I reject it or I let you as an editor do as you please' (and no this is not made up. I've seen referee responses of this form. They also do not bother to use capital letters.)

3) Frontiers has a presence in social media, which targets a younger audience that uses social media effectively.

4) Frontiers counts the impact of each paper more thoroughly -- they go beyond the number of citations. You can see the number of views, social buzz, and the demographics of your audience.

And the only down side is ...
It is generally not free publish in frontiers. Note that it is free to publish as part of this topic and also that many journals cost money including Physical Review Letters and the Astrophysical Journal. I have been lucky enough to be supported by universities that pay these fees.

My last two technical articles are in Frontiers:

1. Explicit equations for a self-gravitating stellar collapse (note that all three authors are women and that this is my most mathematical paper to date). See my blog post on stellar collapse and time travel.

2.  general relativity as a tool to measure planetary spin in space-craft timing signals. See the planetary spin blog post on this paper to learn that planets spin faster than black holes.

Note: I opted to use my children's drawings to illustrate this post because it's what I have. Edward drew these women/girls with excitement that is visible on their faces. It's how scientists are. The words are allegoric. Women do shake the fields they are in (of course, we all shake the space-time when we dance), and some of their energy is sucked by the hardships faced, which are amplified by the gender gap. Marie Curie is the most famous example of a woman scientist, but there are so many other talented women out-there who shine today. I hope to see some of them publish in this topic in Frontiers.

Sunday, November 19, 2017

A belated introduction of Mrs. Edwina Cleverbrain, Mrs. Davina Cleverbrain and Ms. Jemsina Cleverbrain

From left to right: Snow, Lady David, Edward, and Lady Edward
This summer we spent the equivalent of $80 on ... goats. Mihai purchased them at my request from the village of Tormac. Their family had gone to work in Italy and was dismantling their farm. So, In June 2017, Snow White (the Lady James or Jemsina Cleverbrain), Snow White Five Years later (the mother of Snow White; also known the Fairest of them all or as the Lady David, Mrs. Devina Cleverbrain), and the genius goat (the Lady Edward or Ms. Edwina Cleverbrain) have joined our family.

Lady Edward and Lady David are like most mothers: friendly, highly intelligent and provide the best milk I have ever tasted. David milks them twice (and sometimes three times) a day. They are too amazing for words -- when one considers my writing ability. They are, however, described in almost every sentence Edward writes for his homework. 

My phone's collage of Edward (at a petting zoo & this summer)
Andy is not too happy with our naming scheme or with my latest acquisition. He said that he will leave me and never return if I buy a cow. This summer he spent his time helping the children milk the goats -- during and in-between gravitational wave detections -- AND claiming not to remember which one is Lady Edward and which one is Lady David (He also does not know whether he/LIGO is seeing black holes or boson stars; nobody knows that yet for sure.) His job was to hold the goats still, but before running to catch them he always asked us to tell him the colour of the goat he was after. Their colours are really very plain. One is white and the other is grey. In his school writing Edward  refers to his goat as 'Edward -- the goat' or 'Goat Edward'.  He mostly has to write in German and told me 'Frau Edward' would sound too strange for school, and I solemnly agreed.

The Genius Goat can open knots with her mouth and use a fork. She was observed to steal David's cup with left-over rice pudding, which had extra sugar and cacao in it. She put it gently on a a box, and started to take stuff out of the cup with David's fork. The door did not close well and to prevent the goats from coming inside and eating the grain (or sitting on my bed) we tied it with a knot. After I closed the gate as I was driving out with the children, we saw Lady Edward climb on her hind legs and gently open the knot with her mouth. Lady David is bigger, and very strong. She mostly pushes stuff with her head. Snow White climbs everywhere -- it's because she is the lightest. She can even climb on the car.

Edward turned seven this summer. David is ten, and little James just turned one. I stopped writing dedicated birthday posts. The children and our animals take so much care that I have not had the energy to write much before today, but tonight I could not sleep.  So, today after re-lighting the fire, I felt the need to write and not for useful, precise, science writing. I should, however, try to get some sleep to have the strength to wake up soon enough to take on the new day with school, animals and a one-year old AND people coming to install central heating (this time it's gas based). I promise to write more later ... after I do some work on boson stars and take some better pictures of David and his goat/the goats. I will first re-check the fire.

Update: The goats have new names so that they can enrol in school if they desire to or so Edward says. He also said his goat seemed so familiar when he first saw her at the farm because he had known  her from a previous life. She was his sister then and they immediately recognized each other. In the previous weeks he had thought he was a tortoise who lived very long and was too heavy to be taken and eaten by humans, but he is now certain he was a goat.

The former Lady Edward is now Mrs. Edwina Cleverbrain, the former Lady David is Mrs. Davina Cleverbrain, and the former Lady James is Ms. Jemsina Cleverbrain. I asked what grade they would be in, and he said they cannot be confined in a grade and they ought to be free to roam the whole school area. I can talk to the principal about enrolling them, but then I'd have to be responsible for taking more beings to school and it would get even harder to get everyone ready in the morning. I have, however, updated this post accordingly. I hope it is not too confusing. Those of you who find the naming scheme confusing would I am sure sympathize with Andy --- and perhaps prefer to seeing the ladies unglamourously referred to as 'the grey goat' and 'the white goat'.

Thursday, November 9, 2017

Measuring Planetary Spin from Spacecraft Timing

Exploring spacetime with general relativity


The trajectory of NASA's Juno Mission
General relativity is slowly becoming a tool that teaches us about the objects that curve spacetime instead of a hindrance to be corrected for. Planets are heavy and bend the fabric of spacetime affecting the orbits of satellites that go around them and the paths of light sent. Knowing very precisely when the light arrived, and when it was sent is part of space-craft timing. For Juno and Cassini this timing is already sensitive to higher order general relativistic effects like frame dragging. In the future, such measurements could be used to determine the spin of planets to within a percent, which can tell us about their interior. For missions in eccentric orbits relativistic effects are kick-like and can only be observed when the satellite is within a few hours of its pericentre.  We argue that instead of performing cumulative frame dragging measurements over many orbits as was done for Earth, high eccentricity missions like Juno and Cassini need the specific time dependence of each relativistic effect to aid in recovery.

A few words about gravity...

Bent spacetime affecting the orbit of a satellite & the light it sends
General relativity is the theory of gravitation. It says we live in four dimensions -- 3 spatial and 1 temporal -- and that space and time are connected. Gravitation itself is a consequence of the curvature of the spacetime. A planet is heavy and curves the spacetime around it causing it to seem like it pulls objects towards/around it.  This is gravity.

Redshift contribution from frame dragging for Juno. Zoom in.
Looking at relativistic effects
Missions like Juno and Cassini present new possibilities for measuring relativistic effects around the giant planets in our solar system. Relativistic effects are amplified if the orbit of the satellite is eccentric because the spacecraft moves faster and the satellite passes by the planet very closely where the gravitational field is stronger.  This coupled to the larger size of the planet causes frame dragging accelerations that are a few hundred times larger than those near Earth. Since the effects are larger, they might be easier to detect than around Earth.

Most planets have higher spins than black holes. The angular momentum per unit mass for black holes is less than 1, whereas for planets it can be of order hundreds. Earth has a spin on about 800 while Saturn's is about 1000. Precise frame dragging measurements can constrain planetary spin providing an independent estimate of the internal structure of the planet. This structure is relatively uncertain for the gas giants, which are believed to have an internal core of unknown size that rotates at a different rate than the surface.

 We simulate the trajectory of a satellite in a curved spacetime and find the path of the light it sends to receiving stations on Earth. Both follow 'straight lines' in their spacetime also called geodesics. The dynamics of a satellite orbiting a planet can largely be described by Newtonian physics with general relativity providing only small contributions.  The equations of motion are expanded in velocity orders to separate Newtonian and relativistic effects.

The biggest general relativistic effect is time dilation. GPS satellites are sensitive to time dilation and correct for it -- if they would not, the GPS would be off by about 10 km every day. Moving clocks tick slower than stationary clocks. So do clocks in a gravitational field. The ground station has its own time dilation and the difference between its tick signals and those arriving from the satellite are known as the redshift. We compute this redshift for satellites around Earth (Galileo and a proposed mission in an eccentric orbit) and for eccentric orbits around Jupiter (Juno) and Saturn (Cassini). Galileo satellites and the Atomic Clock Ensemble in space -- an ensemble of two atomic clocks that will be placed on the International space station in 2018 -- provide an even better measurements of time dilation, which tests the equivalence principle.

We are interested in higher order relativistic effects like frame dragging in which a spinning mass drags the spacetime in its vicinity affecting any orbiting satellite. The orbital plane of the satellite precesses about the spin axis of the planet. Historically, this effect was first predicted by in 1918 by Einstein, Lense and Thirring. They studied Amalthea, the third moon of Jupiter, and found that it precesses by 1'53'' per century.

Existent Measurements of frame dragging 
Orbital perturbations due to frame dragging have been measured using laser ranging by LARES and LAGEOS. Gravity Probe B measured the effects of frame dragging on the orientation of onboard gyroscopes. The effect is typically averaged over multiple orbits. It is then buried in much larger non-relativistic precession making it very hard to identify the relativistic contribution. E.g., Mercury's observed precession is mostly due to Newtonian planetary perturbations with the relativistic contribution being only about 7% of the total.

Relativistic effects for the Juno orbiter
Instead of averaging we compute each higher order relativistic effect as a function of time and find that they alter the orbit in a kick-like manner at the pericentre. For Juno the kick due to frame dragging could be measured for about two hours. We argue that technology has advanced enough so that we might be able to filter out these effects if we knew their specific time dependence.



This post summarizes results of:

Andreas Schaerer, Ruxandra Bondarescu, Prasenjit Saha, Raymond Angelil,  Ravit Helled and Philippe Jetzer, "Prospects for measuring Planetary Spin and Frame dragging in Spacecraft Timing Signals", Frontiers in Astronomy 4, 11 (2017).

Please read our article for more details.



Sunday, October 22, 2017

Observing gravitational waves AND light from the same source

artist conception
It's been so exciting to see, hear and read through the physics news in the past week that I have not had time to write! More gravitational waves have been detected and this time telescopes have seen light emitted from what's believed to be the closest observed merger of compact objects to date. The collision happened 130 million years ago, when dinosaurs still roamed the Earth, in a galaxy from the Hydra constellation. LIGO has seen gravitational waves from this inspiral on August 17, 2017.  The event was made public on October 16 together with a suite of technical articles.

Edward and his goats
Those of you who know us might guess Andy has been pretty stressed out this summer, but also excited and proud. I was mostly in charge of the children, house repairs and the many animals we have acquired -- taking time off now-and-then to prepare a talk and a fellowship application. Our son, Edward, had a gravitational wave appear on his birthday (the binary black hole also seen by VIRGO) and the neutron star merger 3-days later. So, a picture of Edward next to that of the gravitational waves is somewhat appropriate. His 3-goats also sneaked in the picture. The announcement happened while we were celebrating Edward Seidel's 60th birthday.

What happened on August 17, 2017? The first light from this event was picked up by Fermi's Gamma Ray Burst monitor. Independently, LIGO Hanford saw the event, LIGO Virgo saw nothing, LIGO Livingston saw a huge glitch, which meant data would have been removed around it if there had been no event. The Hanford detector triggered. When the trigger was checked, they saw that Fermi has seen gamma rays some two seconds after LIGO saw the merger of the neutron stars.  Gravitational waves travel at the speed of light towards Earth to shake LIGO's mirrors, while light moves slower through air than vacuum (and is delayed when passing near massive objects), which makes it travel a bit slower. The short time delay meant it could be from the same event, but they had to find its location to be sure.

The waveform was long with the highest signal to noise ratio observed to date. It looked like the first neutron star - neutron star collision or the first neutron star - black hole collision was observed. The strength of the signal meant the colliding stars were close to Earth. So, it was important to get the localization as accurate as possible and look for other kinds of light with all telescopes that could see it.

After running a code developed by Andrew Lundgren at the LVC meeting in 2010 to remove huge  glitches, they uncovered the signal in LiIGO Livingston. The fact that Virgo saw nothing meant the event was near one of its blind spots.  It took four more hours of work to obtain sky localization. When the location was out it was not night in Chile yet, and so scientist spent time planning observations. 

Telescopes might have ignored  the event altogether if LIGO had not seen it because the burst of radiation from the colliding neutron stars was off-axis, i.e., it was not pointed towards Earth. This is why this very close collision was not bight in Gamma rays. It may be that we have missed other sources like this before. Yet only when gravitational wave observatories run for longer we'll be able to tell.

Days later Chandra saw X-rays at this sky location, and telescopes are still observing radio waves. So, stayed tuned for more!!! It will also take time to analyze and understand the data.

The US LIGO detectors are upgrading. If they succeed in reaching design sensitivity, they could see up to an event a week in a year or so. The down side is that we'll miss detections in this period. I wish they could let one detector running in the US and LIGO Virgo, while upgrading the other.

All gravitational waves signals seen to date (LIGO collaboration)
Where was Andy when the universe burped emitting gravitational waves? We were celebrating Edward's seventh birthday belatedly. So, Andy was in Chizatau - in Transylvania. He was watching his computer screen while cooking in our lightless kitchen. This kitchen has no window, but we can leave the door open for light. If the door is open, we can hear noise from the main road (lots of trucks) and the goats. So, the lightless state is at times preferred. I took the children swimming to let him work and cook. When we returned, he was very animated. Nothing was burning in the kitchen. So, while I knew he was not allowed to tell me until the official announcement, I thought this must have been the first gravitational wave LIGO has seen while we were in Chizatau.  We've seen gravitational waves from a black hole binary on August 14, but black holes are...well... black... and this time the universe thought we needed light!  

To remember: Let your children dream! Today one can observe the universe while cooking in Transylvania, and lead/work with a multi-national collaboration after-and-before goat milking! (Many thanks to LouAnne Lundgren for pointing this out).

Note:  The LIGO collaboration has about 1000 people -- many of whom I am proud to call my friends. Work was done in collaboration with observers and with theorists (more friends and people I respect) for this event. I don't mean to take credit or discredit work done by others. This is simply meant to be a fun personal post.