Other Solar systems

Hello Everyone!

In my last post, I talked about what stars were. In this post I will talk about other solar systems and what is involved with what's out there.

The first thing that we will talk about is how other solar systems are located. The most common method is Doppler spectroscopy, a technique that has located around 90 % of exoplanets. It uses radial velocity measurements through examining Doppler shifts in the spectrum of a star around which the planet orbits. Astronomers look for tiny changes in a star’s radial velocity. For example, Jupiter causes the sun to change velocity by about 13 metres per second over a period of 12 years. By tracking these changes over time, astronomers can estimate a planet’s minimum mass.

Another way to identify an exoplanet is to watch the brightness of a parent star. If it dims for a short time, it could indicate a transit – a planet crossing in front of the star. This has been the second most useful method of discovery, but it does lead to a number of false positives. In addition, some astronomers use astrometry – pinpointing the position of a star in the sky and seeing how it makes tiny changes in its positing, which could indicate a planet nearby. This is called star wobbling.

The next point that we will talk about is what an AU actually is. In astronomy, you may have heard it here or there, something is so many AU away, etc. AU is actually short for Astronomical Unit. It is 149,597,871km or the distance from the Earth to the Sun.

Convert the following AU to km.

1. 23
2. 86
3. 47
4. 92
5. 12

Figure 1: An example of other solar systems and comparing them to our own.

The third and final point that we will be talking about today is deep space probes. Do you remember names like Pioneer, Explorer, Mariner, Venera, Luna, Ranger, Voyager, Zond, or Surveyor? Many of the early probes launched by the United States and the former Soviet Union have borne these names. Soon after the Soviet Union launched the first artificial satellite, Sputnik 1 on 4 October 1957, both the former Soviet Union and the United States began to launch a flurry of probes to the Moon, Mars and Venus.

So, just what is a space probe, anyway? A space probe is an un-piloted spacecraft that is used to make observations and send information back to Earth regarding these observed objects. While many satellites are also space probes, we will be discovering those which have escaped earths gravity. These probes carry sophisticated equipment, such as infrared sensors, radars, ultraviolet sensors, magnetometers, soil analysers, spectrometers, and sensors to study wind velocities or chemical compositions. They are various cameras, navigation, and communications systems. There also has to be a power supply and protection against heat, cold, and cosmic radiation. Exactly what equipment is on any deep space probe, of course, depends upon its mission.

Answers to previous questions:

1. Yes, close one eye and pick an object, now switch eyes. Has it moved? That is parallax.
2. Alpha Centauri, Algol, Beta Lyrae

Research Questions:

1. What is the most successful deep space probe so far?
2. What is the largest planet found outside the solar system?
3. What does the space telescope COROT do?
4. What is the smallest planet found outside the solar system?

Q:What did the alien say to the garden?

A: Take me to your weeder!

Enjoy! :)

Emily.

Stars, What are they?

Hello Everyone!
Last post, we talked about the life cycle of stars, so this time we are going to talk about what stars actually are and all the 'gritty' details.

Stars are given two different types of magnitudes, absolute and apparent magnitude. Absolute magnitude is the actual brightness of the star while apparent brightness is what the star looks like from a distance (Earth).

Stars are classified by the Hertzsprung-Russell diagram. The Hertzsprung-Russell diagram (HR diagram), named after Ejnar Hertzsprung and Henry Russell, is a graph which astronomers use to help us understand stars. Across the bottom we plot the stars temperature and down the side we plot the stars’ absolute magnitude. By charting stars this way we begin to see at pattern. A star’s temperature and colour depends directly on how big the star is. The bigger a star is the hotter it will be. This is because the stronger gravity of larger stars causes them to burn their fuel more quickly raising the stars temperature. The stronger an objects gravity is, the more power it has to pull its mass inward. This causes the core to be very compact and creates a lot of extra pressure. This extra pressure builds up, raising the temperature of the core. The hotter the core gets, the more of its hydrogen fuel it will burn.

THIS LINK shows an interactive HR diagram.
Answer the following questions:

1. At what age does the example star first enter the main sequence?
2. At the stage of Red Giant, how large (according to the diagram) is the star
3. What is the example given for the White Dwarf?
4. What is the age used for stellar death (in the example)?

The next topic, eclipsing binary stars, is of particular personal interest to me. THIS LINK shows a binary star system simulator. (It's really fun and interesting to play with). 

Set the simulator to the following settings and record you observations about the light curve placed just above the settings. Why do you think this happens?

1. Star 1 with a Mass of 85, radius of 17, and Temperature of 45000K.
2. Star 2 with a Mass of 85, radius of 17 and temperature of 45000K
3. Separation at 60.00
4. Eccentricity at 0.44

The majority of starts are not single stars, they come in pairs of two or more stars (even in star clusters, containing thousands of stars – globular clusters), orbiting around a common gravitational centre and following Kepler’s Laws. Some stars are easy to detect, others require different measures for detection. On the night sky, some stars may appear to be a binary star system, but they are coincidentally placed close to each other.

At first, astronomers thought all stars simply appeared to be double stars, but in 1902 Sir William Herschel discovered that many of the stars that appeared close to each other actually had changed in position relative to each other. Binary stars that can be distinguished through an optical telescope are called visual binaries. An example of an optical binary is the Mizar in the northern hemisphere, which is the second star to the left in the handle of the constellation The Big Dipper, or more precisely: Usae Majoris, The Big Bear.

Figure 1: Mizar using Stellarium

 Mizar (figure 1) is actually a binary system which can be distinguished with the naked eye, and is a fine target for amateur astronomers who wish to test their eyesight. The second component of the star is called Alcor, or Mizar B (figure 2). 

Figure 2: Mizar and Alcor using Stellarium

Later studies have revealed that both stars are in turn binaries, which makes the entire Mizar complex a system of FOUR STARS! (figure 3) 

Figure 3: Mizar Binary using Stellarium

The discovery was made using spectroscopy, which is a method used to detect unseen companions. Binaries discovered with the method are called spectroscopic binaries. When detected, it is relatively easy to calculate the mass of the binary star system, which is more difficult for single stars. The closest star to our sun, located 4.6 light years away is Proxima Centauri, which is actually a system of three stars. Alpha Centauri is the brightest of the three.

Figure 4: A star being pulled into a black hole.

Binary star systems can vary greatly and are very interesting to study. Each component can have an affect on the other partner’s course of life. Systems containing a white dwarf can display a nova, which is an energetic explosion, which can be seen at great distances. Other systems, may contain a neutron star, or even a black hole, which strips off gas from its companion star. The gas is accelerated towards the compact object and heated to more than 1,000,000°K, which is enough to produce X-Rays! (figure 4)

Variable stars are stars that change brightness. The brightness changes of these stars can range from a thousandth of a magnitude to as much as twenty magnitudes over periods of a fraction of a second to years, depending on the type of variable star. Over 150,000 variable stars are known and catalogued, and many thousands more are suspected to be variable.

There are a number of reasons why variable stars change their brightness. Pulsating variables, for example, swell and shrink due to internal forces. An eclipsing binary will dim when it is eclipsed by a faint companion, and then brighten when the occulting star moves out of the way. Some variable stars are actually extremely close pairs of stars, exchanging mass as one star strips the atmosphere from the other.

The different causes of light variation in variable stars provide the impetus for classifying the stars into different categories. Variable stars are classified as either intrinsic, wherein variability is caused by physical changes such as pulsation or eruption in the star or stellar system, or extrinsic, wherein variability is caused by the eclipse of one star by another, the transit of an extra solar planet, or by the effects of stellar rotation.

Figure 5: Parallax

Parallax is the optical illusion that two stationary points change in position relative to each other, due to a difference in position of the person viewing them. The two points in question will be different distances from the observer and the illusion of parallax is cause by the fact that light, follows straight lines (figure 5). When the observer views the nearer point, the line of his vision toward that point is at given angle within the full arc of his vision. For example, let us say that the view straight ahead is zero degrees, and one point, near the observer, is at minus five degrees while a point which is farther away is at minus two degrees. The apparent angular distance between the points is a subjective three degrees to the viewer. If the viewer moves ten metres to his right, the angular direction to the nearer object, as it is on a shorter radius, will change more than the angular direction to the farther object. So, for instance, when the angular direction to the nearer object is at minus ten degrees, the farther object may only have moved to minus three degrees. Now the subjective angular difference in position is seven degrees. The objects appear to have moved relative to each other.

Answers to previous research questions:

1. No, they haven't been proven.
2. Red, yellow, white, blue
3. Nuclear fusion is when two or more lightweight atoms join together to from one heavier nucleus, with any energy released due to the conversion into nuclear energy.
4. Orion Nebula
5. Orion Nebula

Research Questions:

1. Can/Do we use Parallax in our everyday lives?
2. What are some other Binary star systems?
3. Draw your own HR Diagram with the following stars, Bellatrix, Betelgeuse, Sirius, Altair, Maia, Navi and Vega

Q:Why didn't the dog star laugh at a joke?

A: Because it was too Sirius!

Cheers :)

Emily.

Star Life Cycle

Hello everyone!

In the past couple of posts, we have talked about some of the beginning and endings of a stars life. In this post we will talk about its life cycle.

Figure 1: A simple version of a stars life cycle. Click to enlarge.

A star’s life cycle is determined by its mass. The larger the mass, the shorter the life cycle. Figure 1 shows an extremely simplified version of this cycle. A star’s mass is determined by the amount of matter that is available in its nebula, the giant cloud of gas and dust in which it is born. Over time, gravity pulls the hydrogen gas in the nebula together and it begins to spin. As the gas spins faster and faster, it heats up and is known as a protostar. Eventually the temperature reaches 15,000,000 °C and nuclear fusion occurs in the cloud’s core. The cloud begins to glow brightly. At this stage, it contracts a little and becomes stable. It is now called a main sequence star and will remain in this stage, shining for millions or billions of years to come.

As the main sequence star glows, hydrogen in the core is converted into helium by nuclear fusion. When the hydrogen supply in the core begins to run out, the core becomes unstable and contracts. The outer shell of the star, which is still mostly hydrogen, starts to expand. As it expands, it cools and glows red. The star has now reached the red giant phase. It is red because it is cooler than it was in the main sequence star stage and it is a giant because the outer shell has expanded outward. All stars evolve the same way up to the red giant phase. The amount of mass a star has determines which of the following life cycle paths it will take after the red giant phase.

MEDIUM STARS

Throughout the red giant phase, the hydrogen gas in the outer shell continues to burn and the temperature in the core continues to increase. At 200,000,000 °C the helium atoms in the core fuse to form carbon atoms. The last of the hydrogen gas in the outer shell is blown away to form a ring around the core. This ring is called a planetary nebula. When the last of the helium atoms in the core are fused into carbon atoms, the medium size star begins to die. Gravity causes the last of the star’s matter to collapse inward and compact. This is the white dwarf stage. At this stage, the star’s matter is extremely dense. White dwarfs shine with a white hot light. Once all of their energy is gone, they no longer emit light. The star has now reached the black dwarf phase in which it will forever remain.

MASSIVE STARS

Once massive stars reach the red giant phase, the core temperature increases as carbon atoms are formed from the fusion of helium atoms. Gravity continues to pull carbon atoms together as the temperature increases forming oxygen, nitrogen, and eventually iron. At this point, fusion stops and the iron atoms start to absorb energy. This energy is eventually released in a powerful explosion called a supernova. A supernova can light up the sky for weeks. The temperature in a supernova can reach 1,000,000,000 °C. The core of a massive star that is.


1.5 to 4 times as massive as our Sun ends up as a neutron star after the supernova. Neutron stars spin rapidly giving off radio waves. If the radio waves are emitted in pulses (due to the star’s spin), these neutron stars are called pulsars. The core of a massive star that has 8 or more times the mass of our Sun remains massive after the supernova. No nuclear fusion is taking place to support the core, so it is swallowed by its own gravity. It has now become a black hole which readily attracts any matter and energy that comes near it.

Answers to previous questions:

1. (Your own answers)
2. Latin for cloud
3. 1054 AD (by Chinese astronomers)
4. Dark Nebula
5. When planetary nebulae are formed, how fast do they expand?

Research/Review Questions:

1. Do black dwarves actually exist?
2. Order hottest to coldest, the colour of stars.
3. What is nuclear fusion?
4. What is the closest nebula to earth?
5. What nebula is the sun theorised to have come from?

Q: Why couldn't the astronaut see?
A: He had a twinkle in his eye.

Enjoy, :)

Emily.