Profile

Cover photo
Ngumi Mirie
Lives in Nairobi
154 followers|36,055 views
AboutPostsPhotosVideos

Stream

Ngumi Mirie

Shared publicly  - 
 
 
Now this is scary
Ocean Eats SCUBA Diver
4 comments on original post
1
1
Ngumi Mirie's profile photo
Add a comment...

Ngumi Mirie

Shared publicly  - 
 
 
Testing Relativity With Fast Radio Bursts

A fast radio burst (FRB) is a short burst of intense radio energy originating from outside our galaxy. We aren’t sure what causes FRBs, though the likely candidate is a white dwarf or neutron star falling into a black hole. They only last a few milliseconds, which makes them a challenge to study, but their brief duration may also allow us to test the limits of general relativity.

The foundational idea of general relativity is known as the principle of equivalence. On a basic level it states that two objects of different masses should fall at the same rate under the influence of gravity. The principle is necessary to equate the apparent force of gravity with a curvature of spacetime. So far all tests of the equivalence principle have confirmed it to the limits of observation, but there’s an interesting catch. Since relativity also states that there is a connection between mass and energy, the equivalence principle should also hold for two objects of different energy. Specifically, two beams of light with different wavelengths (and therefore different energies) should be affected by gravity in the same way.

We know that the path of light is changed by the curvature of space (an effect known as gravitational lensing), but the curvature also affects the travel time of light from its source to us (known as the Shapiro time delay). According to relativity, the amount of curvature and the time delay shouldn’t depend upon the wavelength of light. This means we can in principle use FRBs to test this idea.

Since FRBs only last milliseconds, they provide a sharp pulse of light at range of frequencies. If relativity is correct, then the pulse we observe won’t be affected by gravity. If the equivalence principle is wrong, then shorter wavelengths of radio waves from the burst could arrive at a different time than longer wavelengths. We already see different wavelengths arrive at different times due to the interaction between the radio waves and the interstellar plasma in our galaxy, but we know from other observations how much that shift should be. The key is to test whether there is an additional shift not accounted for by standard physics.

Relativity is an extremely well-tested scientific theory, so I wouldn’t count on FRBs showing an energy-based effect, but it’s great that we could have yet another way to test our model. It’s a win-win, since we’ll either confirm our theory yet again, or we’ll discover something new to explore.

Paper: Y. F. Huang & J. J. Geng. Collision between Neutron Stars and Asteroids as a Mechanism for Fast Radio Bursts. arXiv:1512.06519 [astro-ph.HE] arxiv.org/abs/1512.06519
Fast radio bursts are strange bursts of energy originating from outside our galaxy. Their short duration means they could be used to test the limits of general relativity.
27 comments on original post
1
Add a comment...

Ngumi Mirie

Shared publicly  - 
 
 
Is The Sun Losing Mass

Yesterday’s post about Earth’s changing mass raised similar questions about the Sun. In the Sun’s case we know that it’s losing mass, and at a rate fast enough that it’s forced us to change the way we measure astronomical distances.

The Sun loses mass in two major ways. The first is through solar wind. The surface of the Sun is hot enough that electrons and protons boil off its surface and stream away from the Sun, generating a “wind” of ionized particles. When those particles strike Earth’s upper atmosphere they can produce aurora. The solar wind varies a bit in intensity, but from satellite observations we know that the Sun loses about 1.5 million tonnes of material each second due to solar wind.

The second way the Sun loses mass is through nuclear fusion. The Sun fuses hydrogen into helium in its core, producing its life-giving glow over billions of years. The production of helium transforms some of the hydrogen’s mass into energy, which radiates away from the Sun in the form of light and neutrinos. By observing just how much energy the Sun radiates, and using Einstein’s equation relating mass and energy, we find the Sun loses about 4 million tonnes of mass each second due to fusion.

So the Sun loses about 5.5 million tonnes of mass every second, or about 174 trillion tonnes of mass every year. That’s a lot of mass, but compared to the total mass of the Sun it’s negligible. The Sun will keep shining for another 5 billion years, and by that time it will have lost only about 0.034% of its current mass.

While the amount of mass loss is negligible, it isn’t zero, and it has an effect on Earth’s orbit. As the Sun loses mass its gravitational pull on the Earth weakens over time. As a result, Earth is receding slightly from the Sun. Because of solar mass loss the Earth’s distance from the Sun increases by about 1.6 centimeters per year. In astronomy, one of the ways we measure distance is through the astronomical unit, which has traditionally been defined as the distance from the Sun to the Earth. For most of astronomical history the changing distance of Earth was too small to consider, and so the astronomical unit could be considered a constant. But over time our measurement of this distance has become astoundingly accurate, and currently has a precision of about 3 parts per billion. This is accurate enough to observe the gradual increase in distance. So in 2012 the astronomical unit was defined as fixed constant. As a result the Earth is slightly more than 1 astronomical unit away from the Sun.
The Sun is losing mass, and at a rate fast enough that it's forced us to change the way we measure astronomical distances.
70 comments on original post
1
Add a comment...

Ngumi Mirie

Shared publicly  - 
 
 
How A Planet’s Distance Affects Its Formation

Earlier I noted that the presence of ammonia on Ceres was evidence that the dwarf planet formed further away from the Sun than it is now. The reason for that is that the material surrounding a young protostar varies significantly by distance.

The basic structure of a young solar system is that of a protostar surrounded by a protoplanetary disc. As the young star begins to shine, the surrounding disk is heated. Naturally, the material closer to the star gets warmer than the material farther away. In the close region, volatiles such as water and ammonia are broken apart or pushed outward by solar wind. As a result, material in an inner solar system will tend to be more dry and rocky, while the colder outer region will be more wet and icy. Dividing these two regions is a frost line or ice line. Closer than the frost line material is too warm for ice to form. Farther than the frost line ice can form more readily.

In the current solar system, the frost line is at about 5 AU, which is a bit closer than Jupiter, so currently all the rocky planets are inside the frost line, and all the gas giants are beyond the frost line. This would seem to imply that it’s the frost line that determines whether a rocky or gas planet will form. But we now know that things are more complicated than that. For one, the frost line in the early solar system was only about 3 AU, since the gas and dust of the protoplanetary disc absorbed light, keeping outer regions cooler. For another, we know that different planets form at different rates, and they can migrate during their formation. Large, Jupiter-like planets tend to form early on, and they tend to drift inward as they form. Our solar system with its inner rocky planets and outer gas planets seems to be more the exception than the rule.

It does seem that large gas planets will tend to originate beyond the frost line, and this may in fact mean that asteroid belts will tend to form in the region near the frost line. As larger planets form just beyond the frost line, their gravity would tend to disrupt a region in such a way that planets can’t form. This is how our own asteroid belt formed (rather than from an exploded planet as some have claimed).

The dynamics of planetary formation are complex, and there is still much we don’t understand, but we do know that the type of material making up a body shows the history of its formation. Presence of ammonia on Ceres shows that it must have spend time beyond the ice line. In that way it seems more connected to the outer region of the solar system.

Paper: Rebecca G. Martin, et al. Dead zones around young stellar objects: dependence on physical parameters. MNRAS 420 (4): 3139-3146 (2012)
The distance of a young planet around its star affects the way in which the planet forms.
30 comments on original post
1
Add a comment...

Ngumi Mirie

Shared publicly  - 
 
 
Distant Planet May Have Blue Skies

Earth is famous for its blue skies. It gets it blue skies through an effect known as Rayleigh scattering. When light from the Sun collides with an air molecule, it is scattered. The closer the wavelength of light is to the size of the air molecule, the more likely it is to be scattered. Because air molecules are smaller than the wavelength of light in the visible spectrum, long wavelengths (more red) tend to scatter less than short wavelengths (blue). Since blue light is scattered more than red, we tend to see the sky as blue from all the scattered sunlight. This is also why sunsets tend to be red. When the Sun is low in the sky, most of the blue light is scattered by the atmosphere, leaving a red sunset.

Not all planets have a blue sky. Mars, for example, with its much thinner atmosphere has more of a brown sky. Rayleigh scattering is a subtle effect, so it’s been difficult to observe beyond our solar system. But recently a team has observed Rayleigh scattering in the atmosphere of a planet about 100 light years away.

The planet, known as GJ 3470b, was discovered in 2012 through the transit method. That is, as the planet passes in front of its star we observe a slight dimming of the star. The amount of dimming tells us about the size and orbit of the planet. From transit observations we know GJ 3470b is a Neptune-sized planet with an orbital period of about 3 days. But if we can only observe the planet by its effect on starlight, how do we know there is Rayleigh scattering in its atmosphere?

To do this the team used a rather ingenious technique. They analyzed the brightness dip of the star during a transit at different wavelengths, and found that the calculated size of the planet increased at shorter wavelengths. In other words the planet appears larger at blue wavelengths than it does at red. This makes sense if the atmosphere is Rayleigh scattering light. Red light isn’t scattered much, so at red wavelengths only the planet itself blocks light from the star. Blue light is strongly scattered, so it doesn’t reach us, so effectively both the planet and its atmosphere block light at blue wavelengths.

Just because Rayleigh scattering occurs in the atmosphere of GJ 3470b, we shouldn’t assume its atmosphere is Earth-like. Given its size the atmosphere is likely hydrogen and helium rather than our nitrogen-oxygen mix. But this is a great example of how we’re starting to study the atmospheres of alien planets.

Paper: Diana Dragomir, et al. Rayleigh Scattering in the Atmosphere of the Warm Exo-Neptune GJ 3470b. The Astrophysical Journal, Volume 814, Number 2 (2015)
Recently a team has observed Rayleigh scattering in the atmosphere of a planet about 100 light years away.
53 comments on original post
1
Add a comment...

Ngumi Mirie

Shared publicly  - 
 
 
Triangulum II: A Dark Matter Galaxy?

Dark matter is far more common in the universe than regular matter. Since it interacts gravitationally like regular matter, there has been speculation that some galaxies may contain lots of dark matter, but very little visible matter. These “dark galaxies” wouldn’t be particularly bright, but they would be distinguished by their strong gravity. We’ve found some evidence of dark matter galaxies before, and now a new paper proposes that Triangulum II could be a dark galaxy.
We've found some evidence of dark matter galaxies before, and now a new paper proposes that Triangulum II could be a dark galaxy.
51 comments on original post
1
Add a comment...
Have him in circles
154 people
Sanmon  Chege's profile photo
Allen Carr Books's profile photo
Neema Wamui's profile photo
Ken Muasya's profile photo
The Husband Chronicles's profile photo
Kd Vince's profile photo
Jenny Pan's profile photo
Joseph Munyonyi's profile photo
Charles Maingi's profile photo

Ngumi Mirie

Shared publicly  - 
 
 
Brighter Than Twenty Galaxies

A superluminous supernova is an immense supernova more than ten times that of the type Ia supernovae used to measure cosmic distances. They are so intense that they challenge our understanding of just how they occur. Two possible mechanisms include the idea that they may be caused by magnetic heating as the core collapses into a magnetar, or that it’s intensity is strengthened by pair-instability reactions in its core. The evidence leaned toward the magnetar model, but observations of a new supernova challenge that idea.

The new supernova is known as ASASSN-15lh, and it was more luminous than any supernova ever seen. About 20 times more luminous than the entire Milky Way. It’s light has traveled for about 2.7 billion years, so it’s apparent brightness in our sky wasn’t particularly bright, but in terms of absolute magnitude it was about three times as bright as other known superluminous supernovae. It is also unusual in that it occurred in a bright galaxy where there is not much new star formation. Other superluminous supernovae occur in active dwarf galaxies.

The team observing the spectra of this supernova found that it was low in hydrogen. This is indicative of a star that has cast off its hydrogen-rich outer later, and would seem to support the magnetar model. But the extreme energy of ASASSN-15lh puts it at the upper limit of the model. If this was indeed a magnetar supernova, then it was at the upper limit of the hypothetical energy range. That seems a bit unusual, and it raises the question of whether the magnetar model might be flawed.

The key to solving this mystery will be the discovery of similar superluminous supernovae. This particular supernova was discovered by the All Sky Automated Survey for SuperNovae (ASASSN) which is a collection of small (14 centimeter) telescopes in Chile and Hawaii. It’s a relatively low cost project that lays the groundwork for larger projects such as LSST. So over time we’re bound to find similar supernovae.

Paper: Subo Dong, et al. ASASSN-15lh: A highly super-luminous supernova. Science Vol. 351, Issue 6270, pp. 257-260 (2016)
A supernova known as ASASSN-15lh is more luminous than any supernova ever seen.
48 comments on original post
1
Add a comment...

Ngumi Mirie

Shared publicly  - 
 
 
Relative Units

In an earlier post I talked about the astronomical unit, and how it was standardized in 2012 because the old definition (the distance from the Earth to the Sun) was gradually increasing due to the Sun’s loss of mass. It turns out that’s not the completely correct story.

Using radar telemetry we can measure the astronomical unit to an accuracy of a few meters. In my earlier post I had stated the accuracy was 3 parts per billion, but that wasn’t quite right. In 2009 the IAU defined the astronomical unit to be 149,597,870,700 meters, with an uncertainty of 3 meters. Since the change in distance due to the Sun’s mass loss is only about 1.5 centimeters, it would seem an uncertainty of 3 meters is too large for the Sun’s effect to make a difference.

It turns out that analysis of telemetric data for the solar system seemed to point toward a change in the astronomical unit of about 15 meters per century, which is much larger than the effect of the Sun. But other observations haven’t confirmed such a drift, and so the result remains highly controversial.

So why did the IAU adopt a fixed standard for the astronomical unit? In the actual 2012 resolution, the possible drift due to the Sun’s mass loss is listed as one reason, but the main reason was the need for self consistent units in the framework of general relativity. The big problem is not the Sun’s mass loss, but the fact that (because of relativity) an astronomical unit when measured by a spacecraft orbiting Jupiter is different than one made when orbiting Earth. When all of our measurements were made from Earth, relativity didn’t play a big role. But we now have a flotilla of spacecraft across the solar system, so relativity is an issue.

So now the astronomical unit is 149,597,870,700 meters exactly by definition. The Earth’s distance from the Sun is pretty close to that, but your results may vary depending on where you are in the universe.

Paper: Krasinsky, G. A., Brumberg, V. A. Secular increase of astronomical unit from analysis of the major planet motions, and its interpretation. Celest. Mech. Dynam. Astron. 90 (3–4): 267–288 (2004)
So why did the IAU adopt a fixed standard for the astronomical unit?
41 comments on original post
1
Add a comment...

Ngumi Mirie

Shared publicly  - 
 
 
Is Earth Gaining Mass Or Losing Mass

We generally think of the Earth as having a constant mass. On a basic level that’s true, but the Earth’s mass does change very slightly. So is it’s mass increasing or decreasing?

Earth gains mass through dust and meteorites that are captured by its gravity. If you watched the recent meteor shower you know this can occur on a regular basis. In fact from satellite observations of meteor trails it’s estimated that about 100 – 300 metric tons (tonnes) of material strikes Earth every day. That adds up to about 30,000 to 100,000 tonnes per year. That might seem like a lot, but over a million years that would only amount to less than a billionth of a percent of Earth’s total mass.

Earth loses mass through a couple of processes. One is the fact that material in Earth’s core undergoes radioactive decay, and therefore energy and some subatomic particles can escape our world. Another is the loss of hydrogen and helium from our atmosphere. The first process only amounts to about 15 tonnes per year, but the loss from our atmosphere amounts to about 95,000 tonnes per year.

So it’s most likely that Earth is losing a bit of mass each year, but if the rate of meteors is on the higher end of estimates, then it could be gaining a bit of mass.
59 comments on original post
1
Add a comment...

Ngumi Mirie

Shared publicly  - 
 
 
Titan As An Earth-like World

We don’t generally think of Saturn’s moon Titan as an Earth-like world. It has no breathable atmosphere, and with a surface temperature of about 90 Kelvin life as we know it is out of the question. But there are many parallels between Titan and Earth, and so we can see the moon as a kind of colder, smaller cousin to our own planet.

Both Earth and Titan have thick nitrogen atmospheres. Earth’s also has about 20% oxygen, but the atmospheric dynamics are similar. On Titan, methane plays a similar role to water on Earth. Titan has clouds, rain and large lakes or seas. It has seasons following the changing tilt of its orbital plane relative to the Sun. As a result, the terrain of Titan is interestingly similar to Earths, with rivers, flood plains, and mountains. It even has ice volcanoes, and so is geologically active.

Because of its lower temperature, and the way methane obscures visible light, we have to look in the infrared to see much of these details. A recent image by the Cassini mission does just that. Shown below, the false-color image gives infrared wavelengths more Earth-like hues. The result is Titan as an Earth-like world. It’s a great example of how sometimes a world so different from our own can also be hauntingly similar.
there are many parallels between Titan and Earth, and so we can see the moon as a kind of colder, smaller cousin to our own planet.
22 comments on original post
1
Add a comment...

Ngumi Mirie

Shared publicly  - 
 
 
The Crab Nebula

The Crab Nebula is a pulsar that’s only about 1,600 light years away. It is the remnant of a supernova that occurred in 1054, and was recorded by Chinese astronomers. Pulsars are rotating neutron stars that produce bursts of energy we observe as pulses. Most pulsars are observed at radio wavelengths, but the Crab Nebula pulsar can also be observed in the visible. Because of its relative proximity, it’s also one of the few neutron stars we can observe directly. You can see it as the bright central dot in the x-ray image above.

When the supernova occurred in 1054, it had a maximum magnitude of about -6, which is much brighter than the brightest stars in the sky, and even brighter than Venus at its maximum. It should have been easily visible across the globe, and yet there is limited confirmed recording of the event in historical records. There are some hints of recordings, but the Chinese observation is the only one with sufficient accuracy to confirm. It’s an interesting example of how transient events in the sky didn’t always gain attention.

One of the mysteries about the Crab Nebula is that the calculated mass is about 3 solar masses. Combined with the mass of the neutron star itself (about 2 solar masses), the estimated mass of the original star would be about 5 solar masses. However to create a supernova of this size and chemical composition, the original star should have been about 9 – 11 solar masses. We’re still not sure where the missing mass went, though a good possibility is that the outer layers of the star were pushed away by the star before the supernova occurred. We see this happen with Wolf-Rayet stars.

The Crab Nebula itself can be seen with the naked eye, and some of its structure can be observed with binoculars or a small telescope. So if you get the chance, it’s worth checking out.
The Crab Nebula is the remnant of a supernova that occurred in 1054 AD.
26 comments on original post
1
Add a comment...

Ngumi Mirie

Shared publicly  - 
 
 
On Dark Matter And Dinosaurs

Let me begin by saying there is no evidence that dark matter killed the dinosaurs. None whatsoever. Unfortunately the idea was posted on Nature’s blog, and from there it went to Scientific American and elsewhere. The various social media took the story and it has spread like a prairie wildfire. The actual preprint is much less sensational (and doesn’t mention dinosaurs) but it is still very speculative.

The idea comes from the fact that the Sun does not follow a flat orbit around the galaxy. Instead, its motion wobbles above and below the galactic plane, crossing the galactic plane every 35 million years. This isn’t unusual, as lots of stars follow similar paths, but it has led some to speculate that perhaps this periodicity could explain periodic mass extinctions in the geologic record.

The problem is, there isn’t any strong evidence for cyclic mass extinctions. Some analysis of the data has hinted at a pattern, but the correlation isn’t very strong. Of course that hasn’t stopped people from proposing everything from companion stars to Nibiru to explain these periodic extinctions. There been similar proposals that every time the Sun crosses the galactic plane the Oort cloud would be disrupted, causing comets to sweep into the inner solar system and bombard the Earth.

What’s new here is that the authors propose that dark matter within the plane of the galaxy is doing the disrupting. As I wrote about last week, there is a hint of dark matter seen in gamma ray observations of the center of our galaxy. One model that could account for these gamma rays is type of dark matter that would lie within the galactic plane. So if this type of dark matter exists, and if it disrupts the Oort cloud when the Sun crosses the galactic plane, and if that caused comets to fling into the inner solar system and bombard the Earth, and if that bombardment caused periodic mass extinctions, then you should see some evidence in the geologic record.

So what evidence is there? None. Well, not quite none. If you assume the model is true, and then look for a periodicity in the cratering record of Earth, you find that the cratering record agrees with the model about three times better that it agrees with random cratering. Scientifically, that isn’t very convincing data. It makes for a mildly interesting paper, but it’s mostly speculation at this point.

But Nature and several other websites have decided to take this speculative idea, add the word dinosaurs to the title, and imply that scientists are proposing dark matter killed the dinosaurs. No one is proposing that. It’s link-bait noise that makes the job of communicating real science all that more difficult. So if you see one of these sensationalized titles, don’t share it on social media. Tell your friends that share the articles that it’s speculative nonsense. Hopefully we can drown this noise and get back to real science.

Because honestly, science is interesting enough without the hype.

Paper: Lisa Randall, Matthew Reece. Dark Matter as a Trigger for Periodic Comet Impacts. arXiv:1403.0576 [astro-ph.GA] (2014).
There is no evidence that dark matter killed the dinosaurs. None whatsoever. It's link-bait noise that makes the job of communicating real science all that more difficult.
24 comments on original post
1
Add a comment...
People
Have him in circles
154 people
Sanmon  Chege's profile photo
Allen Carr Books's profile photo
Neema Wamui's profile photo
Ken Muasya's profile photo
The Husband Chronicles's profile photo
Kd Vince's profile photo
Jenny Pan's profile photo
Joseph Munyonyi's profile photo
Charles Maingi's profile photo
Collections Ngumi is following
View all
Basic Information
Gender
Male
Story
Tagline
Origin.The ancient Egyptian name,Meri-Amun,meaning "beloved of the sun god Amun"when adopted by the Isralites was recorded in the bible as Miriam.The sister of the famous Moses who led the Isralites to the promised land of Canaan was called Miriam.The Latin adopted the name as Maria which form appears in most Western European languages.Mary is the English Bible Version.The Ethiopia versions Maryam and Mariam unlike in Europe where it is a female baptisimal name have been used as patronymics/surnames for ages.Some examples of well known Ethiopians with the patronymic are;Emporor Takla Maryam(1430-1433) of the Solomonic Dynasty,Emporor Baeda Maryam (1468-1478) and more recently Mengistu Haile Mariam who was head of state between 1977 and 1991.And the current Ethiopian Prime Minister HailleMariam Desalegn.The introduction of the name to giküyüland(Central Kenya)came about either in the late 1700s or early 1800s during the period in Ethiopian history reffered to as Zamana Masafint or" Era of the Prince" when there was protracted conflicts between the many claimants of the seat of the emporor populary known as the king of kings(Nègusa Nagäst)Among the group of royals who escaped the terror of Ras Sehul the powerful Tigrean Warlord were several women with the title Waizero.One of the women,escorted by some men among them Kassa and Tefere reached an area now known as Dagorreti and settled there.The woman was carrying a boy whose name was Mariam which the Agiküyü adopted as Miríí.Though Waizero was a title(Married Woman or the equivalent of Dame in the court titles of Ethiopian Nobility) the Agiküyü were not to know that and they called her Waithera,so,the boy grew up to be known as Miríí wa Waithera and is the originator of the family by the name Mbari ya Mirie.The boy is my anscestor and it is partly the reason why I have a fairer skin color than most kikiyus.
Bragging rights
Able to relate to matters of science while lifting weights.I know a thing or two about the origin of the universe and at my weight of 152lbs(70 Kgs) My PB deadlift is 330lbs(150 Kgs) and I am aiming a bit higher than that.
Places
Map of the places this user has livedMap of the places this user has livedMap of the places this user has lived
Currently
Nairobi