New Nearby Stars Discovered

[Sikon]

SPACEDAILY

Twenty New Stars In The Neighborhood
by Staff Writers
La Serena, Chile (SPX) Nov 15, 2006

Astronomers have identified 20 new stellar systems in our local solar neighborhood, including the twenty-third and twenty-fourth closest stars to the Sun. When added to eight other systems announced by this team and six by other groups since 2000, the known population of the Milky Way galaxy within 33 light-years (10 parsecs) of Earth has grown by 16 percent in just the past six years.

The discoveries were made by a group called the Research Consortium on Nearby Stars (RECONS), which has been using small telescopes at the National Science Foundation's Cerro Tololo Inter-American Observatory (CTIO) in the Chilean Andes since 1999. These new results will appear in the December 2006 issue of the Astronomical Journal.

"Our goal is to help complete the census of our local neighborhood and provide some statistical insights about the demographics of stars in our galaxy - their masses, their evolutionary states, and the frequency of multiple star systems," says RECONS Project Director Todd Henry of Georgia State University in Atlanta. "Due to their proximity, these systems are also excellent targets for exoplanet searches, and ultimately, for astrobiological studies of whether any planets that are found could support life."

The 20 newly reported objects are all red dwarf stars, which now comprise 239 of the 348 known objects beyond our Solar System within the 10-parsec boundary of the RECONS survey. Thus, red dwarfs likely account for at least 69 percent of the Milky Way's residents.

"Red dwarfs are among the faintest but most populous objects in the Milky Way," Henry explains. "Although you can't see a single one with the naked eye, there are swarms of them throughout the galaxy."

The distances to these stars were measured via a classic trigonometric parallax technique using the 0.9-meter telescope at CTIO. The parallax technique for measuring the distance to a star takes advantage of the simple geometry of Earth's changing position in the cosmos as it orbits the Sun each year. The apparent back and forth motion of a nearby star during the year reflects the motion of the Earth around the Sun, much like how your finger appears to jump back and forth in front of your eyes if you blink one eye, then the other.

From Earth, nearby stars appear to make tiny ellipses in the sky because the Earth does not jump from one side of its orbit to another, but slides smoothly around the Sun. The extreme points of the Earth in its orbit are much like the positions of your eyes in your head, and the size of the apparent motion of your finger depends on how close you hold it to your eyes - when nearer, it seems to jump more, relative to distant background objects.

With observations over several years, it is possible to make parallax measurements with an accuracy of 1 milliarcsecond (0.0000003 degrees), or about one two-millionth the width of the full Moon. This allows astronomers to measure distances accurate to better than 10 percent out to more than 300 light-years.

The team of astronomers includes Henry, Wei-Chun Jao, John Subasavage and Thom Beaulieu of Georgia State University, Phil Ianna of the University of Virginia in Charlottesville, and Edgardo Costa and Rene Mendez of the Universidad de Chile. The RECONS long-term parallax program began under the auspices of the National Optical Astronomy Observatory (NOAO) Survey Program in 1999, and continues via the Small and Moderate Aperture Research Telescope System (SMARTS) Consortium.

"We expect to announce more systems within 10 parsecs in the future," notes Henry. "The pool of nearby stars without accurate parallaxes is nowhere near drained."

The purpose of this survey is to discover and characterize overlooked stars and brown dwarfs in the vicinity the Sun. Objects are scrutinized by measuring their positions (and wobbles), their brightnesses and colors, and by taking spectroscopic fingerprints to examine their atmospheric composition. The estimated "missing" population of solar neighborhood members is expected to be composed primarily of very low mass stars with spectral type M (known as red dwarfs), and objects of spectral types L and T, many of which are actually brown dwarfs with too little mass to start long-term thermonuclear reactions.

These L- and T-dwarfs shine feebly, glowing only because of energy leaking out since their gravitational formation, many billions of years ago. RECONS has also found several nearby white dwarfs, which are the burned-out cores of intermediate- mass stars, lurking in the solar neighborhood.

The Chilean members of the team have been supported by the Fondo Nacional de Investigacion Cientifica y Tecnologica and the Chilean Centro de Astrofisica. The team from the United States has been supported by NASA's Space Interferometry Mission, the National Science Foundation, and Georgia State University.

One wonders if there is a chance Proxima Centauri is not the closest star, if even more nearby dim dwarf stars may have been overlooked for decades. The minimum distance for interstellar travel may not be 100% guaranteed to be 4.2 light-years.

[Solauren]

Of course, nearby stars (say less then 4 light years), really, really raises the possibility of a probe to another solar system.

We'd just need a 10% Light speed drive

[Howedar]

No, the possibility is still essentially zero. Do you have any idea what such a rocket would require?

[Gil Hamilton]

No, the possibility is still essentially zero. Do you have any idea what such a rocket would require?

With modern technology and over a shortish time period, that is.

[Fingolfin_Noldor]

Well... what you need is something that can ramp up the speed to 10% over say a few months to a year and let inertia do the work.

Technology is there, only thing is costs.

[Sikon]

There are concepts for unmanned interstellar probes propelled by lasers, microwave beams, or particle beams. Weight can be as little as a few kilograms or less while still returning data using tricks like having the reflector for communication as well as propulsion. Sail concepts are typically extremely big but extraordinarily thin and lightweight, to still intercept the beam despite dispersion at trillions of kilometers distance.

Typically the minimum beam power to send a suitable interstellar probe to 0.1c to 0.2c or more is on the order of 10GW to 100GW. If a close dwarf star was luckily found, power required to send a probe to reach it with the same number of years in transit would be inversely proportional to distance squared, so every light-year matters. A terrestrial 1GW nuclear power plant can be built for $1 billion, although use of space solar power would be more likely. Inefficiency of the laser or beam source could increase the total power needed up to a few times.

One discussion is here.

The above is only for lightweight probes. A manned colonization mission is less a possibility in the near-future, as it would tend to cost too many trillions of dollars unless nuke-pulse propulsion was used, as near-future lasers are many orders of magnitude more expensive per unit of energy delivered. However, beam propulsion is the option with minimum capital cost for a miniature unmanned probe.

[Howedar]

Problem of note: You'll be buzzing through the target system at that same .1-.2c. The quality of data you're going to get in such a case, especially with respect to how much the mission would cost, is pretty poor.

[Sikon]

Problem of note: You'll be buzzing through the target system at that same .1-.2c. The quality of data you're going to get in such a case, especially with respect to how much the mission would cost, is pretty poor.

Yes, a fly-by mission is the easiest.

Still, slowing down is possible. One method sometimes proposed is to use two reflectors. When the target star is approached, one reflector bounces the beam back to hit the backside of the original reflector. Magnetic braking is another proposal. Admittedly, slowing down would add to the complexity and cost of the mission.

Either way, not a huge amount of scientific equipment is likely to be carried given extreme mass constraints.

Although some interesting scientific data would be gained, the first interstellar mission might potentially be mostly a "proof-of-concept," mainly just sending something to another star.

Such wouldn't be unprecedented. For example, although scientific data was returned from the Apollo missions, few would argue that the real main motivation for the U.S. going to the Moon in 1969 was scientific research. Lots of people today don't even think interstellar travel is possible, so it would be impressive.

Fancier missions could come later.

[SyntaxVorlon]

Well... what you need is something that can ramp up the speed to 10% over say a few months to a year and let inertia do the work.

Technology is there, only thing is costs.

The cost would be the fuel equivalent of the mass of the sun.

[Sikon]

Well... what you need is something that can ramp up the speed to 10% over say a few months to a year and let inertia do the work.

Technology is there, only thing is costs.

The cost would be the fuel equivalent of the mass of the sun.

I'm not sure what you mean to reference. However, probably you refer to the exponential inefficiency of hypothetically trying to reach much of lightspeed with a chemical-fueled rocket, with the number of stages approaching infinity. I don't think anybody suggests such for interstellar travel, and definitely Fingolfin_Noldor didn't do so.

For an unmanned lightweight beam-propelled interstellar probe, I illustrated the relatively moderate power needed in my post after Fingolfin_Noldor's post. It is equivalent to some number of modern-day nuclear power plants but not an astronomical number.

For a vastly more massive manned colonization rocket, the most likely option would be nuke-pulse propulsion unless superior technology is developed in the future. For example, an Orion starship proposal described here would mass initially 0.5 million metric tons, having an unloaded mass of 0.1 million metric tons, traveling about 1 light-year per 30 years. Given the nature of the proposal, that almost surely also includes deacceleration at the end. Admittedly, with that performance (effective specific impulse), if one wanted to travel at 10% lightspeed instead of 3.3%, a much higher initial to final mass ratio than 5:1 could be needed, i.e. a multi-stage design. However, it still isn't too astronomical. Dyson's design would use 300,000 pulse units, but they wouldn't have to cost more than hundreds of thousands of dollars each or less in mass-production.

Of course, total costs could be far more than the pulse-unit expense. For example, developing an industrial civilization "seed" that could expand with human labor indefinitely from only some thousands of tons initial mass could be challenging. One is unlikely to be so lucky as to go to a star system with an earth-like planet, so most likely all equipment would need to operate off asteroids, comets, etc. However, developing such isn't impossible...

[K. A. Pital]

For a vastly more massive manned colonization rocket, the most likely option would be nuke-pulse propulsion unless superior technology is developed in the future.

How about a massive maser-propelled solar sail? Is it beyond our technological capabilities, even, say, with freely used nanotubes?

[dragon]

Look at probes like SMART-1, Deep Space 1 and the delayed JIMO. All of wich used Ion engines to attain a good velocity. The JIMO probe unlike the other two uses a nuclear batery to provide the neccessary power. Other concepts such as the laser propulsion and solar sails are also viable systems the would work.

[Sikon]

For a vastly more massive manned colonization rocket, the most likely option would be nuke-pulse propulsion unless superior technology is developed in the future.

How about a massive maser-propelled solar sail? Is it beyond our technological capabilities, even, say, with freely used nanotubes?

Maser sails seem within technological capabilities possibly developed within decades, but they couldn't be very massive within the foreseeable future.

One concept investigated has been the Starwisp. It illustrates that practical mass may be limited by beam dispersion and the maximum beam intensity a sail can handle. Limited acceleration time, distance, and hence momentum transfer may be possible before the maser beam disperses too much, even with a large sail. Nanotubes might allow mesh of miniscule mass per unit area, but I don't know how to determine what acceleration time and distance would become practical.

It is easier to calculate a theoretical upper limit on maximum mass possibly accelerated by a given beam power. For that, treat a sail as intercepting approximately the whole beam at any range needed with near-perfect reflection. In that case, each gigawatt-year of microwave beam energy is 3.15E16 joules, delivering up to 2.1E8 kg * m/s of momentum effectively upon reflection. For example, that means each metric ton accelerated to 10% lightspeed would require at least 140 gigawatt-years of microwaves. That is the ideal before inefficiencies. The easiest comparison is present-day world electrical generation of 2000 gigawatts, but realistically the concept could be to have relatively cheap, powerful future space solar power satellites.

However, the above is only a theoretical upper limit on the possible mass to power ratio. Unfortunately, actual performance obtainable could be vastly less, due to the other limits mentioned in the article. It's hard to compete with nuke-pulse propulsion for very massive payloads, short of self-replicating technology or other very major advancements. A lightweight probe is easier for all beam propulsion.