Monday, June 29, 2020
Wednesday, June 24, 2020
Neutron stars and stellar black holes are the final stages of evolution for large stars – with black holes being more massive than neutron stars. In theory, the maximum mass of a neutron star is about 2.1 solar masses. However, there is some indirect evidence that more massive neutron stars could exist. There is little evidence for the existence of black holes smaller than about 5 solar masses, leading to a mass gap in our observations of these compact objects.
What is intriguing about the August 2019 merger – dubbed GW190814 – is the mass of the smaller object, which appears to fall within this gap. “Whether any objects exist in the mass gap has been an ongoing mystery in astrophysics for decades,” says Charlie Hoy of the UK’s Cardiff University, who played a key role in analysing data from the detection and writing the paper that describes the observation, which has been published in The Astrophysical Journal Letters. “What we still don’t know is whether this object is the heaviest known neutron star or the lightest known black hole, but we do know that either way it breaks a record.”
The actual paper is available to be read for free here since it is an open access article.
Like I had said to the students in my astronomy classes, this is going to go down as the golden age of astronomy. Since the beginning of human history, we only had light as our only detector of the heavens. Now, we have not only neutrinos and high-energy cosmic rays, but also gravitational waves as our means to look at the heavens. We have three different and separate ways to look at our sky!
 R. Abbott et al., The Astrophysical Journal Letters,896:L44(20pp), 2020.
Tuesday, June 23, 2020
Monday, June 22, 2020
It is not surprising to me. I've been expecting it, and in some ways, I've been preparing for it. I mentioned earlier that I've enrolled in Quality Matters courses to give me formal training and credentials in running online and hybrid courses. I just finished the first workshop, and I have one more to do with them before I do the last required course with my own institution.
I must say that the one course that I've completed so far was more useful than I initially expected. There were a few "eye-opener" moments that I never realized before. It is one thing to anticipate and guess what a student needs from an online course, it is another when one actually goes through it, and are shown some of the best-practice methods of online education from the point of view of the student.
At the end of the first course, I realize that what I've learned was not only useful for the next time I have to teach a remote or online course, which will be this Fall most likely, but I'm going to take what I've learned to also improve my face-to-face courses, whenever I get to teach one. I know that many of the things I put on the Learning Management Systems can be reorganized better, because if it is suitable for online students, then it certainly is appropriate for face-to-face students.
But of course, one of the unique challenges with teaching a science course is labs, and how one can effectively do such a thing with a remote class. I've been looking at material put out by Pivot Interactives, which looks promising. I attended one of their webinars, and I like the way they show the experiments. I intend to sign up for the instructor trial version during the next week or so to check them out further. Do you have any experience with using them, either as a student or as an instructor? If you do, I'd love to hear from you.
There are more challenges unique to teaching math and science online, and I'm going to explore them during the next few weeks. I'll post them here whenever I encounter them, and maybe you might have an idea on the best-practice way to tackle them.
Friday, June 12, 2020
New "free fall" measurement in extreme high gravitational field has upheld one of the foundations of General Relativity. This time the measurement comes from a white dwarf orbiting a neutron star (a pulsar). A neutron star is a star that has huge gravitational field, so this is an amazing testing ground for GR under extreme condition.
"Above all, it is the unique configuration of that system, akin to the Earth-Moon-Sun system with the presence of a second companion (playing the role of the Sun) towards which the two other stars 'fall' (orbit) that has allowed to perform a stellar version of Galileo's famous experiment from Pisa's tower. Two bodies of different compositions fall with the same acceleration in the gravitational field of a third one."
"The pulsar emits a beam of radio waves which sweeps across space. At each turn this creates a flash of radio light which is recorded with high accuracy by Nançay's radio telescope. As the pulsar moves on its orbit, the light arrival time at Earth is shifted. It is the accurate measurement and mathematical modeling, down to a nanosecond accuracy, of these times of arrival that allows scientists to infer with exquisite precision the motion of the star," says Dr. Guillaume Voisin.
You can get free access to the actual paper here.
Thursday, June 11, 2020
The ISS is useful after all! :) Physicists have created the first controlled Bose-Einstein condensate in low earth orbit, thus eliminating the issue of gravitational effects that affects the stability of the condensate.
A review of the work can be found here.
As discussed, Bose–Einstein condensation requires low temperatures, at which atoms hardly move. However, when a BEC is released from a magnetic trap so that experiments can be carried out, repulsive interactions between the atoms cause the cloud to expand. Within a few seconds, the BEC becomes too dilute to be detected. The expansion rate can be reduced by decreasing the depth of the trap, and, thereby, the density of atoms in the trap.
On Earth, the planet’s gravitational pull restricts the shape of possible magnetic traps in such a way that a deep trap is needed to confine a BEC (Fig. 1a,b). By contrast, Aveline and colleagues found that the extremely weak gravity (microgravity) on the International Space Station allowed rubidium BECs to be created using shallow traps. As a result, the authors could study the BECs after about one second of expansion, without needing to manipulate the atoms further.
But this is more than just an achievement on the scientific level. It is also a technological feat because of the numerous requirements that are needed to be able to have an experiment on the ISS, as stated in the review:
Aveline and colleagues’ technological achievement is remarkable. Their apparatus needed to satisfy the strict mass, volume and power-consumption requirements of the International Space Station, and be robust enough to operate for years without needing to be serviced. The authors’ Earth-orbiting BECs provide new opportunities for research on quantum gases, as well as for atom interferometry, and pave the way for missions that are even more ambitious.
If you have ever designed an experiment, you know of all the issues involved, not just the scientific ones. This includes engineering, robustness, economics/costs, etc. So I can't imagine what they had to come up with to be able to send something up there and basically run this with very little to no involvement from the astronauts onboard.
Very well done indeed!
 D.C. Aveline et al. Nature v.582, p.193 (2020).
Thursday, June 04, 2020
It's interesting that in the list of funding agencies, NASA is absent. This goes to show you that many of these research activities that seem to be "astronomy-related" are not the sole domain of NASA. In fact, the area of particle-astrophysics is more closely related to particle physics than astronomy.
The video didn't clarify explicitly that in looking at the "spectrum" of light from each of these celestial bodies, one gets the radial velocity of these bodies with respect to us (i.e. via the amount of redshift), not its distance from us. That last piece of information can only be "deduced" using the radial velocity and the Hubble equation, i.e. the Hubble constant, a number that is still being refined.
Still, this new telescope is going to be quite exciting in revealing more of the mysteries of dark energy.