News Items and Content of a general nature
- Research sheds new light on intelligent life existing across the Galaxy (15/06/20)
A new study led by the University of Nottingham and published today in The Astrophysical Journal has taken a new approach to this problem. Using the assumption that intelligent life forms on other planets in a similar way as it does on Earth, researchers have obtained an estimate for the number of intelligent communicating civilizations within our own galaxy -the Milky Way. They calculate that there could be over 30 active communicating intelligent civilizations in our home Galaxy.
Nottingham University Press Release : LINK
Astrophysical Journal abstract : LINK : Space – Magazine article : LINK
- As many as 6 billion Earth-like planets in our galaxy, according to new estimates (16/06/20)
There may be as many as one Earth-like planet for every five Sun-like stars in the Milky way Galaxy, according to new estimates by University of British Columbia astronomers using data from NASA’s Kepler
Science Daily article : LINK : Astronomical Journal abstract : LINK
- Colliding galaxies created the solar system, say astronomers (12/06/20)
The solar system may have been formed in a long-ago collision between the Milky Way and its orbiting companion the Sagittarius dwarf galaxy. That is the conclusion of astrophysicists in Spain, who have analysed data from the Gaia space observatory.
Physics World article : LINK : Nature Astronomy Paper : LINK
Starlink and Radio Astronomy
AFAIK Starlink will use the 10.7-12.7 GHz : 13.85-14.5 GHz : 17.8-18.6 GHz : 18.8-19.3 GHz : 27.5-29.1 GHz : and 29.5-30 GHz bands.
Radio astronomy has a primary allocation from 10.6 to 10.68 GHz which is directly adjacent to where Starlink operates. This creates two problems: Due to the high sensitivity combined with high gain of radio astronomy receivers, these receivers will most likely be blinded by the starlink satellite whenever one comes into the beam. Furthermore, our experience is that satellite transponders tend to have significant out of band noise so this noise will directly affect the radio astronomy observation. There is a significant chance that the Starlink constellation will render the band allocated to radio astronomy useless. It should also be noted that the band from 10.6 to 10.7 is also used for other science purposes including radiometers on board of satellites.
The FCC has reflected the radio astronomy concerns by ordering:-
In the 10.7-11.7 GHz band, operations must be coordinated with the radio astronomy observatories listed in 47 CFR § 2.106, n.US131, to achieve a mutually acceptable agreement regarding the protection of the radio telescope facilities operating in the 10.6-10.7 GHz band For the purposes of coordination with these listed facilities or the National Radio Quiet Zone, correspondence should be directed to the National Science Foundation Spectrum Management Unit (Email: email@example.com)
This order falls short of what is needed as it does not take into account the worldwide locations of radio astronomy observatories. US131 only lists US-based observatories.
Furthermore, the methanol maser line is at a rest frequency of 12.178 GHz which is inside the band where Starlink intends to operate. Observation of methanol maser lines at that frequency will become impossible.
The frequency range from 14.47 to 14.5 GHz is allocated to radio astronomy. Again, FCC only protects US radio astronomy facilities.
Astropeiler Stockert operates its 10m dish at these aforementioned frequencies and we expect significant interference from the Starlink constellation.
Some concern exists in addition that the satellites may have spurious emissions in L-Band due to the on board electronics. Since a very large number of the satellites are expected to be launched, this may lead to an overall accumulated noise level in protected bands. We have not identified yet any information what levels have been permitted with respect to spurious emissions.
Posted on “firstname.lastname@example.org” by Dr Wolfgang Herrmann
president of the Astropeiler Stockert e.V.( LINK )
This guest post was written by Nathan Wetherell for an assignment in the Fall 2019 Foundations of Modern Astrophysics class taught by Professor Cara Battersby. As part of the course, students were tasked with writing an Astrobite-style summary of a topic in astronomy. Stay tuned for more bites in this series!
Nathan is a second-year mechanical engineering student concentrating in the field of aerospace. After graduation, he hopes to get the opportunity to work for one of the many new private spaceflight companies and is interested in the contributions astrophysics can make to human exploration and spaceflight.
Being the only moons large enough to view with the aid of simple binoculars (besides our own of course), it is no wonder that the four Galilean moons of Jupiter have captured our attention and curiosity since their discovery in 1610. These four moons, Europa, Io, Ganymede, and Callisto have recently moved out of the realm of simple curiosity for the sake of science and into the new focus of human spaceflight: establishing permanent bases. Developing a habitat on another celestial body is no simple task. With the challenges posed by long-duration space travel, the construction of habitats able to withstand extreme environments, and the physiological effects of living in a low gravity environment being of particular concern, the destination must be well worth the investment and struggles of the pioneering astronauts. Living within the influence of Jupiter has its own set of unique challenges stemming mostly from the intense radiation belts that result from the extreme magnetic field output by the gas giant. However, humans are adaptive and willing to take on challenges if nothing else. Instead of allowing these risks to turn us off to the idea of establishing permanent settlements on these moons, the unique features of Io, Ganymede, and Callisto should be analyzed through the lens of viability for inhabitation and their individual challenges viewed as exciting engineering problems to overcome.
is the first of the Galilean moons, with a gravitational acceleration of 1.8 m/s at its surface and a diameter of 3,642 kilometers, it is slightly larger than our moon. That is where the similarities stop, however, as Io is extremely active geologically. In fact, the tidal forces exerted on it by Jupiter make it the most geologically active body in our entire solar system. This attribute results in a smooth, young surface due to the constant flows of lava filling in any past impact craters (as opposed to inactive bodies such as our moon). These tidal forces also create interesting phenomena such as solid tides, where the moon itself bulges and recedes by around 100 meters every day. For comparison, the liquid tides in our ocean only change by a maximum of 24 meters. Yet these high levels of geologic activity and extreme tidal forces are not what make the surface of Io an unlikely candidate for potential human habitation, but rather its proximity to its host planet.
Jupiter’s aforementioned magnetic field and accompanying radiation belts are particularly harmful to Io, where a surface radiation level of around 3,600 rem/day can be measured. One ton of Io’s material is stripped from the surface every second by these belts in a process known as sputtering. This highly ionized material is then picked up by Jupiter’s field, extending the field itself to twice the predicted size. Eventually, these particles come back around and slam into Io and the other Galilean moons with enough energy to easily damage organic and inorganic materials alike. Yet as a product of our destructive tendencies, we have made large advancements in the form of radiation shielding and underground structural design which would be directly applicable to any efforts to establish settlements on Io. While lead has been the radiation shielding material of choice for years, this heavy element would not be practical to carry to bases on Io en masse. Instead, future humans could harness the moon’s silicate-rich soil to create shelters that can withstand the intense radiation. While the exact types of silicates which constitute Io’s surface are not known, research with certain types of silicates has shown promise for their radiation attenuating properties. This physical layer would also work to protect the structure from the nightly condensing atmosphere as Jupiter eclipses the Sun as well as insulating it from Io’s frigid temperatures. As an alternative to burying human structures, the moon’s geologic activity could be taken advantage of by creating shelters in the extensive network of lava tubes hidden beneath the surface. These tubes are theorized to have formed in the same way lava tubes are formed on Earth, with magma flows crusting over and then draining. Not only would these tubes be exceptionally interesting to geologists and volcanologists, but they could provide shelter to future inhabitants from the harsh radiation of Jupiter (provided they are inactive of course).
At 5,264 kilometers in diameter (larger than Mercury but with half its mass), Ganymede has slightly less gravity at its surface than Io and is the largest moon in the solar system. Yet this is not the only title it possesses; it also has the only observable internally generated magnetic field of any moon in our solar system. Theorized to be created in a process similar to the magnetic field of Earth, the rotating molten core of Ganymede allows for this moon to be the only bastion against the continuous tide of radiation captured and circulated by its host planet. Yet this field is a relatively weak 0.72 microtesla compared to the magnetic fields of Earth and Jupiter which stand at 65 and 417 microteslas respectively. This means that while the moon’s field provides some protection of its surface the intensity of these belts results in a yearly natural radiation exposure seven hundred times higher than that of Earth or one hundred times that of Mars. As a result, humans could not inhabit Ganymede in the same way we live here on Earth but would also be more free to roam the surface when compared to the unshielded and more irradiated Io. Instead of being stuck in an exotic lava tube under the surface (which wouldn’t be possible on Ganymede due to its theorized subsurface ocean and lack of geologic activity), one can imagine future humans watching the tiny sun rising over the horizon even if only for a short time.
Seeing Jupiter as the dominant figure in the sky, 36 times larger than our moon appears from Earth, and watching the spectacular polar auroras as the radiation belts break against the moon’s magnetic field would no doubt be a fascinating sight and one that is well worth the engineering effort.
While unremarkable at first glance, Callisto is widely considered the best possible location amongst the moons of Jupiter for surface habitation. This is not due to a particular feature that this planet possesses such as a strong magnetic field but is simply a result of its location. Orbiting at a radius of around 1.9 million kilometers, Callisto is the farthest of the Galilean moons from Jupiter, residing around 1.8 times further from the planet than Ganymede. This simple increase in distance drastically reduces the radiation experienced at this moon’s surface to around 0.01 rem/day, only twelve times more than one would naturally receive here on Earth. As a result, humans could live on the surface of Callisto with just a sufficiently strong radiation attenuating glass between them and the remaining radiation from its host planet. In addition to this relative safety from radiation, this moon is composed of around 40% water. Not only would this be a valuable resource for potential inhabitants, but it could serve as a fuel source for further exploration into the outer solar system.
It is undeniable that the future of human space travel lies in developing permanent habitats on other worlds, even if that future seems distant. While the locations for this effort have already been determined to be the Moon and Mars, the Galilean moons, particularly Callisto, should be next on that shortlist. Not only would the settlement of these bodies be unprecedented achievements for mankind, the knowledge we would gain in the pursuit and realization of this goal would deepen our understanding of the system we inhabit.
AAS meeting questions, 9th September, 2019
1) What are the estimates for how many generations old the sun is?
There are 3 defined populations of stars. Population III formed from the original cosmos and were composed of H and He and are believed to have had a lifetime of 500,000 to a million years. Population II stars formed from the debris of these original stars and therefore have small amounts of additional elements manufactured in the supernova of previous stars. Our sun is relatively young, part of a generation of stars known as Population I, which are much richer than population II stars in elements heavier than helium.
In 2015 a team published a paper claiming that they had identified a very early galaxy that contained population III stars. Cosmos Redshift 7 is at a redshift (z) of 6.6. The galaxy is observed as it was about 800 million years after the Big Bang, during the epoch of reionisation. With a light travel time of 12.9 billion years, it is one of the oldest, most distant galaxies known.
CR7 shows some of the expected signatures of Population III stars i.e. this first generation of stars produced during early galaxy formation. These signatures were detected in a bright pocket of blue stars; the rest of the galaxy contains redder Population II stars.
In order for our sun to have the metallicity (ie heavier elements) it has many stars must have contributed dust and debris to it’s makeup. However, the question “how many generations of stars came before ours” is simplistic. As stars have a range of lifetime stars from different generations would have contributed to our Sol so there will have been much overlap.
I know I quoted 100 generations at the meeting but the simple answer to the simplistic question is “Lots”.
2) What is the status of the EHT (Event Horizon Telescope)?
The latest news, from HERE dated 21st June, is that the Africa mm Telescope has just passed it’s Preliminary Design Review.
As a point of interest Rhodri Evans, now at the University of Namibia, who gave us a talk including the EHT in February 2017, is a member of the telescope project team and chair of the science team. LINK
3) What particles are DAMA/LIBRA detecting for their recent Dark Matter detection claims?
From Symmetry Magazine, a joint publication of the Fermi and SLAC National Accelerator Labs. LINK
“One candidate DAMA is searching for: WIMPs, or weakly interacting massive particles. Sodium iodide crystals in DAMA’s detectors emit bursts of radiation whenever a particle (possibly a WIMP) collides with the crystals’ atomic nuclei. DAMA’s signal shows these bursts occurring in the annual cycle physicists would expect to see”.
Time Dilation and Travelling to the nearest stars
According to the theory of relativity, time dilation is a difference in the elapsed time measured by two observers, either due to a velocity difference relative to each other, or by being differently situated relative to a gravitational field.
As a result of the nature of space-time a clock that is moving relative to an observer will be measured to tick slower than a clock that is at rest in the observer’s own frame of reference.
Ignoring any time dilation due to gravity the following equation can be used to calculate the time dilation at various velocities (www.emc2-explained.info/Time-Dilation/#.Wg8kF0pl-Uk) :-
t1 = t x (1-v2/c2)0.5
t1 = Dilated time frame (time on body moving)
t = Rest time frame (ie on Earth for this example)
v = velocity
c = speed of light, approx 300,000 km/s
The graph for dilated time for a moving object, as a percentage of time for a stationary object is:-
If we have 2 clocks, one on earth assumed to be at rest, and one moving at 0.2c it can be seen the moving clock is running around 2% slower than the rest clock. So, 20 years on earth is equivalent to 19.6 years for the moving clock.
It is not until we get up to speeds that are a large proportion of the speed of light that time dilation becomes significant. For example at 0.75c the moving clock is running at 66% of the rest clock, ie 20 years on earth becomes 13 years on the moving clock.
Should you disagree with my conclusions, or think I’ve made a mistake, please be sure to let me know.
I will post any corrections or alternative ideas on the website.
Hubble Studies Different Stages in the Collision Between Galaxies : Posted 3rd June 2017
The video is here.
The Hubble site Web Page is here.
An image of a galaxy collision captures only one stage of billion year long collision process. This visualization of a galaxy collision supercomputer simulation shows the entire collision sequence, and compares the different stages of the collision to different interacting galaxy pairs observed by NASA’s Hubble Space Telescope. With this combination of research simulations and high resolution observations, these titanic crashes can be better understood.
Credit: NASA (http://www.nasa.gov/), ESA (http://www.spacetelescope.org/), and F. Summers (STScI (http://www.stsci.edu/))
Simulation Data: Chris Mihos (Case Western Reserve University) and Lars Hernquist (Harvard University)
Publication: April 24, 2008
In the News 15th March 2017
Globular Cluster “47 Tucanae”
An interesting item in the news concerns this cluster and, in particular, a white dwarf called X9.
This is a cluster that is some 14,800Lyrs away in the southern sky constellation Tucana. It is the 2nd brightest in the sky, after Omega Centauri in Centaurus, having been discovered in 1751.
The news item relates to a white dwarf, X9, which is in orbit around the black hole in this cluster. It has an orbital period of 28 minutes and is the fastest star found orbiting a black hole, moving at some 12 million kilometres per hour, and is only 2.5 times the distance from the BH as the moon is from earth.
Michigan State University scientists were part of the team that made this discovery, which used NASA’s Chandra X-ray Observatory as well as NASA’s NuSTAR and the Australia Telescope Compact Array.
Some points from this story:-
- This cluster is thought to contain millions of stars and covers an area of sky the size of the moon.
The nearest star to us, apart from the sun, is Proxima Centauri at 4.2Lyrs. If we were in the centre of this cluster there would be 100,000 stars within that 4.2Lyrs.
- Although it used to be thought that Globular Clusters would not be a good place to look for Black Holes this view is changing.
- Although material is being ripped off the white dwarf into the BH accretion disc it is thought that it is not likely to follow it in any time soon as it will move further away as it loses mass.
- The LIGO instrument, looking for gravitational waves, is not sensitive enough to detect these waves from this event but a space based instrument, planned for the 2030s (may be!).
See below for a bit more on gravitational wave sources/detection.
Gravitational Waves – Sources
A bit more detail on the sources and wavelength of gravitational waves is on the website
I have tried to précis the info on the page, go have a look if you want more.
Referring to the picture below, the wavelength is on the bottom axis (longer wavelengths = lower frequency). Marked on the chart are various sources and also the range of current and proposed detection systems.
NS (Neutron Stars): gravitational waves generated by individual neutron stars as they spin.
NSB (Neutron Star Binaries): These are binary systems consisting of two neutron stars.
BHB (Black Hole Binaries): These are binary systems consisting of two stellar mass black holes.
EMRI (ExtremeMassRatio Inspirals): These are compact stellar remnants (white dwarfs, neutron stars, or stellar mass black holes only a few times more massive than our Sun) in the process of being captured and swallowed by a supermassive black hole.
WDB (White Dwarf Binaries): Above the white dwarf stochastic background are a few thousand Individually resolvable white dwarf binary systems in our Galaxy.
SMBHB (SuperMassive Black Hole Binaries): Occasionally two supermassive black hole systems will merge, producing a huge burst of gravitational waves at millihertz frequencies.
Binary background: Random signals arising from thousands of binary systems emitting gravitational waves continuously in overlapping frequency bands.
Relic background: From the Big Bang itself, consisting of quantum fluctuations in the initial explosion that have been amplified by the early expansion of the Universe.
LIGO (Laser Interferometer Gravitational wave Observatory): This consists of an L-shaped vacuum tube 4 kilometres long, with masses hanging at the corner and ends of each arm, carefully shielded
against vibrations or other outside disturbances. A passing gravitational wave changes the relative distances between the masses in the two arms, which can be detected by interfering laser beams travelling along each arm.
Pulsar timing: Pulsars, spinning neutron stars emit beams of electromagnetic radiation, seen as “pulses” when they sweep over the Earth. Since the spin of a neutron star is very stable, these pulses can be predicted and fit with high precision. A passing gravitational wave alters the path length between the pulsar and the Earth, changing the pulse arrival times in a fluctuating manner.
Cosmic microwave background: Long wavelength gravitational waves will have contributed to the density variations in the CMB but analysis is difficult
Advanced LIGO: Continual improvements to the LIGO detectors will result in an order of magnitude improvement in sensitivity.
LISA (Laser Interferometer Space Antenna): A space based LIGO a million time the size of the earth based instrument. It will place three spacecraft in Solar orbit 5 million kilometres apart. The spacecraft would use laser ranging to monitor their relative separations, and thus would be sensitive to changes caused by passing gravitational waves.
Pulsar timing array: Over the coming years it is expected that discoveries of new pulsars, improvements in the precision of pulse timing measurements, and longer observations of pulsars, will result in a dramatic improvement in the sensitivity of pulsar timing to gravitational waves. The “pulsar timing array” refers to this coordinated detection effort.
Question 1) Imaging black holes
It was thought that this referred to the current Event Horizon Telescope project.
To quote the website
“The World’s First Image of a Black Hole : What does a black hole look like? Nobody knows because they are… invisible – not even light can escape. But how do we know they exist when we can’t see the black hole or it’s interior? To answer these questions astronomers are building a virtual telescope the size of the earth to image for the first time in history the ‘shadow’ of a black hole. For this they will use a worldwide network of radio telescopes.”
The shadow in question is the event horizon, the one way membrane around the black hole that marks the point at which light cannot escape. Material that falls into this region emits high frequency radio waves that can be detected by radio telescopes on earth.
Question 2) Gravitational wave sources.
See “In the News” 15th March section, above