What can old stars teach us about the birth of our galaxy?

These needles in the vast galactic haystack take more effort to find, but they help piece together our origins.

ANNA FREBEL: It has always been really important for us humans to understand what our past is. On Earth we do for example genealogy. We ask our parents about our grandparents and so forth to learn about the history. And astronomers do the same thing about the universe. So we are asking the question how did everything begin? How did everything start to evolve? How did everything fall into place so that Earth could form at some point together with our Sun and later as humans we could start to emerge. And so the work that stellar archaeologists are doing is to try asking and answering the question how did the chemical evolution of the universe begin? Which means how did all the chemical elements, how did they form and how were they produced? And we know that they are produced in stars and supernova explosions. All the elements of the periodic table are created in stars and supernova explosions. And we specifically have means with these old stars to reconstruct how each of these atoms, for example, iron atoms or carbon atoms or calcium, how this was all created for the first time in the very first stars about 13.5 billion years ago.

But how do astronomers actually know how old stars are? Well it's actually not that easy because we can't just go – first of all we can't go there and measure an age. And actually age dating in general with various astronomical techniques is very, very complicated. But we can use a different fact to our advantage. As I've said the elements are created in stars and supernova explosions, and there were actually no heavy elements heavier than hydrogen, helium, and lithium present at the very earliest times soon after the Big Bang. But with time and with time I mean over the billions of years since then all the elements were created successively in stars. And so their content has built up over time. Today the universe contains a whole two percent of all these heavy elements that we know in the periodic table, so everything except hydrogen and helium. And we use those facts because we just look backwards and we search for the stars that have the smallest amounts of all of these heavy elements. So we look for example for the most iron-poor stars. We like to use iron as our reference element.

And that takes us back to this very early time when there simply wasn't that much iron in the universe. So in order to determine that a star is old and hence interesting we need to do a chemical composition. We need to determine the chemical composition of the star and we do that with spectroscopy that works very similar to the mass spectrometer in all the TV shows. So we observe the light and it's sent through a prism and that gives us an absorption spectrum and we can measure the absorption lines that appear due to the wiggling of the atoms in the outer atmosphere of the star. And from the line strength we can determine how much of a given element is present in the star.

These stars are extremely rare as you can imagine since they are leftovers from this very early time from soon after the Big Bang. So it takes a lot of effort to find that needle in the galactic haystack. But first I actually have to make clear that these stars are found in our own Milky Way galaxy. They are super super old but they're actually very local. That complements the aspect that most people know about namely the very distant galaxies we call them high ratchet galaxies that are very, very far away and whose light has traveled for millions and billions of years to us. So when we finally detect it we see that galaxy as when it was very young. We have this complementary technique of using old stars and at some point the Milky Way has actually gobbled them up from wherever they're formed and so they are today located in our Milky Way very fairly close on astronomical standards. Only a few thousand light years away perhaps. And that is there where we look for them. It still takes a lot of work sifting through all these stars that formed recently like the Sun but we have a variety of telescopes in place that we regularly use to observe these stars. And it's a sequence of three steps going from smaller telescopes to intermediate size telescopes to the really big telescopes.

So at the moment I'm using mostly the largest telescopes in Chile. These ones are optical telescopes which means we observe visible light. And the telescope that I use there is called the Magellan telescope and it has a 6.5 meter mirror. It's quite big and impressive and I really love going there. Why do I do that? Well it really goes to the heart of what the job of an astronomer is. Collecting data. Sitting in a telescope staring at the night sky. And the fantastic thing in Chile is that the sky is absolutely dark. Actually that's not quite true. The surrounding Earth is really dark. The sky is super bright and it is absolutely marvelous and fantastic to just actually let the telescope do its job and go outside and look at the sky above you and you see the bright band of the Milky Way above you and the myriad of little lights in the sky. And you can even see the galactic center shining very bright and actually you can almost see your shadow. You definitely don't need any moon or any light to walk around. You're not going to walk into a tree or into a car or anything because the combined light from all the stars is so bright that you can orient yourself. This is absolutely fantastic and actually the best part of my job.

From our analysis and comparing our chemical abundance results – so the composition of these stars - with what is supposed to have come out of the very first stars we have actually learned that the very first stars were probably not as energetic in their deaths as previously assumed. And there's a lot of research going on in this area now to figure out what these first stars really were like and how energetic they were which has a lot of ramifications for how everything got started and what kind of role these first stars had in shaping this early time.

  • With billions of stars in our galaxy, why should astronomers seek out the oldest ones?
  • Age-dating stars is a complicated process, so astronomers use chemical compositions, telescopes, and prisms to determine the age of these ancient stars.
  • Some telescopes used for this purpose are in extremely remote places, where you can observe the bright band of the Milky Way with the naked eye.


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Study suggests sperm donation, like organs, should be allowed post-mortem

Is it ethical to use a dead man's sperm to become pregnant?

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  • Many parts of the world are suffering from a shortage of sperm donors due to the high bar for acceptance and varying laws regarding donor anonymity.
  • A recent article suggested that, as a solution, we should consider allowing men to opt-in to posthumous sperm donation, much like men and women do for organ donation.
  • It's technically feasible, but how would we navigate the complex ethical and legal issues surrounding such a proposal?

Can, and should, dead men procreate? Yes and yes, says a recent article published in the Journal of Medical Ethics.

The UK is facing a sperm donor crisis. According to the article, UK sperm banks only take on a few hundred new donors per year, forcing them to import thousands of sperm samples from the U.S. and Denmark, which dominate the global market for sperm donations due to their high supply.

These countries have a high supply of sperm primarily because of laws and regulations protecting the donor's anonymity — in the UK, for instance, babies born from sperm donations are permitted to contact their biological father after they turn 18, an emotional confrontation that dissuades many from donating. In fact, in a 2016 study based in the U.S., 29 percent of current donors said they would have refused to donate if they could not be anonymous.

How can we increase the supply of sperm donors while simultaneously shielding donors from a potentially life-upending confrontation and providing children with the right to know their own ancestry? Allow for post-mortem sperm donations. Men could opt-in to become sperm donors after their death, just like they do as organ donors. So long as they were collected no longer than 48 hours after death, sperm could be collected via surgery or electrical stimulation of the prostate and be frozen for later use.

"If it is morally acceptable that individuals can donate their tissues to relieve the suffering of others in 'life-enhancing transplants' for diseases," wrote the article authors, "we see no reason this cannot be extended to other forms of suffering like infertility."

A legal and ethical quandary?

As it turns out, this idea isn't all that new. The first posthumous sperm retrieval occurred in 1980 after a 30-year-old man suffered a fatal brain injury in a car accident. His family requested that his sperm be preserved, which was done through surgery soon after he had been declared dead.

There have been numerous postmortem sperm retrievals since then, but they've always existed in a legal grey area. For instance, in 1997, a UK man named Stephen Blood caught meningitis, collapsed into a coma, and died soon after. His wife, Diane Blood, had requested that doctors extract two samples of semen from Mr. Blood.

However, the UK's Human Fertilisation and Embryology Authority had forbidden Mrs. Blood from using those samples to become pregnant, as Mr. Blood had passed away prior to giving written consent to the procedure. In the UK posthumous sperm donation is illegal without written consent. After an appeal, Mrs. Blood was permitted to seek fertility treatment outside of the UK and later gave birth to a son.

Other countries, such as France, Germany, and Taiwan, have a full ban on posthumous fertilization. At the same time, countries like the U.S. and Belgium have no legislation on the subject whatsoever. Given the complex legal, ethical, and medical nature of posthumous fertilization, this range of legislative response is not unexpected. For example, is it ethical to collect sperm from an individual who never wanted to procreate in a country where the young population is dwindling and sperm donors are in short supply? Such is the case in many parts of the UK Is it reasonable to collect sperm from donors who have died and who are, by extension, more likely to be older and with less healthy sperm? Is the offspring of a deceased sperm donor considered to be the donor's legal heir?

These and other issues muddy the waters for countries when crafting policies around posthumous sperm donation. However, the authors of the recent Journal of Medical Ethics article argue that allowing for this procedure is at the very least ethically permissible and likely beneficial for society at large.

"The ability to reproduce matters to people and donated sperm enables many people to fulfill their reproductive desires," write the authors. "It is both feasible and morally permissible for men to volunteer their sperm to be donated to strangers after death in order to ensure sufficient quantities of sperm with desired qualities."