Sky & Telescope - February 2021 - 16

Baby Star

Even though it is the
prototype for the entire
class, in many ways it is
not a typical T Tauri star.
follows a rather elliptical orbit around its mate. In the May
2020 Research Notes of the AAS, Rainer Köhler (University of
Vienna, Austria) and Karolina Kubiak (University of Lisbon, Portugal) noted an intriguing pattern. The little star
brightens and fades depending on where it is in its orbit. The
astronomers attribute this behavior to a nearly edge-on dust
disk that is known to surround the two infrared stars. The
disk is more tenuous toward its edge, so when the little star
skirts farthest from its partner, less dust obscures it, and so it
brightens. The two stars will be closest together around 2023.
Unfortunately, no one has weighed T Tauri North, the
one star in the system whose visible light we see, and its
exact nature is uncertain. Even though it is the prototype
for the entire class, in many ways it is not a typical T Tauri
star. For one thing, the star outshines most of its peers. The
high luminosity suggests the star is more massive than most
other T Tauri stars, and in the past astronomers have estimated a mass about twice that of the Sun. T Tauri North has
a disk, but it's nearly face-on, which may be why we can see

High-energy
radiation
from shock

Dust
photosphere

r envelope
Oute

t envelope
Dus
p
st va orized
Du

Protostar
Accretion
shock
Partially
ionized gas

Dust
destruction
front

Infrared
radiation

Not to scale

Most T Tauri stars are young pre-mainsequence stars that were born within
the last several million years and are
less than 2.5 times as massive as the
Sun. T Tauri itself, however, may be an
even younger variety of star, called a
protostar.
Despite their similar names, the two
stellar types - protostars and premain-sequence stars - are different
stages of stellar evolution. A protostar
forms after a clump in an interstellar cloud rapidly collapses under the
force of gravity. Gravity causes material to crash down toward the object's
surface, heating it so much that it
begins to emit light. Thus gravity -
and not nuclear fusion - powers the
newborn star.
New material from the birth cloud

16

FEBRUARY 2 021 * SK Y & TELESCOPE

keeps raining down onto the protostar, increasing its mass. In fact, the
protostar is so shrouded in its dusty
birthplace that no visible light escapes
into space (see diagram above).
The protostar phase is brief. How
brief depends on the star's aspirations:
Just as someone who wants to earn a
PhD has to spend more time in school
acquiring knowledge than someone
who has a high-school diploma, so a
more massive star has to spend more
time as a protostar accreting material
than a less massive star. The Sun's
protostar stage lasted only a few
hundred thousand years. Less massive stars - the vast majority - spend
even less time as protostars.
A powerful wind from the protostar
soon blows away most of its dusty

cocoon, letting the star's visible light
emerge. This metamorphosis marks the
transition from protostar to pre-mainsequence star.
Unlike a protostar, a pre-mainsequence star no longer acquires
much new material. Still, the star keeps
on shining, because gravity gently
squeezes and heats the star. Over
time, thanks to gravity, a pre-mainsequence star shrinks, getting smaller
and smaller.
Most stars spend far more time as
pre-main-sequence stars than protostars. The Sun, for example, was a
pre-main-sequence star for 36 million
years. Less massive stars linger longer,
and the least massive red dwarfs
remain pre-main-sequence stars for
billions of years. Some of the M stars

G REGG DINDER M A N / S&T, SOURCE: S. W. STA HLER / PASP 19 94

Protostar vs. Pre-Main-Sequence Star



Sky & Telescope - February 2021

Table of Contents for the Digital Edition of Sky & Telescope - February 2021

Contents
Sky & Telescope - February 2021 - Cover1
Sky & Telescope - February 2021 - Cover2
Sky & Telescope - February 2021 - 1
Sky & Telescope - February 2021 - Contents
Sky & Telescope - February 2021 - 3
Sky & Telescope - February 2021 - 4
Sky & Telescope - February 2021 - 5
Sky & Telescope - February 2021 - 6
Sky & Telescope - February 2021 - 7
Sky & Telescope - February 2021 - 8
Sky & Telescope - February 2021 - 9
Sky & Telescope - February 2021 - 10
Sky & Telescope - February 2021 - 11
Sky & Telescope - February 2021 - 12
Sky & Telescope - February 2021 - 13
Sky & Telescope - February 2021 - 14
Sky & Telescope - February 2021 - 15
Sky & Telescope - February 2021 - 16
Sky & Telescope - February 2021 - 17
Sky & Telescope - February 2021 - 18
Sky & Telescope - February 2021 - 19
Sky & Telescope - February 2021 - 20
Sky & Telescope - February 2021 - 21
Sky & Telescope - February 2021 - 22
Sky & Telescope - February 2021 - 23
Sky & Telescope - February 2021 - 24
Sky & Telescope - February 2021 - 25
Sky & Telescope - February 2021 - 26
Sky & Telescope - February 2021 - 27
Sky & Telescope - February 2021 - 28
Sky & Telescope - February 2021 - 29
Sky & Telescope - February 2021 - 30
Sky & Telescope - February 2021 - 31
Sky & Telescope - February 2021 - 32
Sky & Telescope - February 2021 - 33
Sky & Telescope - February 2021 - 34
Sky & Telescope - February 2021 - 35
Sky & Telescope - February 2021 - 36
Sky & Telescope - February 2021 - 37
Sky & Telescope - February 2021 - 38
Sky & Telescope - February 2021 - 39
Sky & Telescope - February 2021 - 40
Sky & Telescope - February 2021 - 41
Sky & Telescope - February 2021 - 42
Sky & Telescope - February 2021 - 43
Sky & Telescope - February 2021 - 44
Sky & Telescope - February 2021 - 45
Sky & Telescope - February 2021 - 46
Sky & Telescope - February 2021 - 47
Sky & Telescope - February 2021 - 48
Sky & Telescope - February 2021 - 49
Sky & Telescope - February 2021 - 50
Sky & Telescope - February 2021 - 51
Sky & Telescope - February 2021 - 52
Sky & Telescope - February 2021 - 53
Sky & Telescope - February 2021 - 54
Sky & Telescope - February 2021 - 55
Sky & Telescope - February 2021 - 56
Sky & Telescope - February 2021 - 57
Sky & Telescope - February 2021 - 58
Sky & Telescope - February 2021 - 59
Sky & Telescope - February 2021 - 60
Sky & Telescope - February 2021 - 61
Sky & Telescope - February 2021 - 62
Sky & Telescope - February 2021 - 63
Sky & Telescope - February 2021 - 64
Sky & Telescope - February 2021 - 65
Sky & Telescope - February 2021 - 66
Sky & Telescope - February 2021 - 67
Sky & Telescope - February 2021 - 68
Sky & Telescope - February 2021 - 69
Sky & Telescope - February 2021 - 70
Sky & Telescope - February 2021 - 71
Sky & Telescope - February 2021 - 72
Sky & Telescope - February 2021 - 73
Sky & Telescope - February 2021 - 74
Sky & Telescope - February 2021 - 75
Sky & Telescope - February 2021 - 76
Sky & Telescope - February 2021 - 77
Sky & Telescope - February 2021 - 78
Sky & Telescope - February 2021 - 79
Sky & Telescope - February 2021 - 80
Sky & Telescope - February 2021 - 81
Sky & Telescope - February 2021 - 82
Sky & Telescope - February 2021 - 83
Sky & Telescope - February 2021 - 84
Sky & Telescope - February 2021 - Cover3
Sky & Telescope - February 2021 - Cover4
https://www.nxtbook.com/nxtbooks/aas/st_202207
https://www.nxtbook.com/nxtbooks/aas/st_202206
https://www.nxtbook.com/nxtbooks/aas/st_202205
https://www.nxtbook.com/nxtbooks/aas/st_202204
https://www.nxtbook.com/nxtbooks/aas/st_202203
https://www.nxtbook.com/nxtbooks/aas/st_202202
https://www.nxtbook.com/nxtbooks/aas/st_202201
https://www.nxtbook.com/nxtbooks/aas/st_202112
https://www.nxtbook.com/nxtbooks/aas/st_202111
https://www.nxtbook.com/nxtbooks/aas/st_202110
https://www.nxtbook.com/nxtbooks/aas/st_202109
https://www.nxtbook.com/nxtbooks/aas/st_202108
https://www.nxtbook.com/nxtbooks/aas/st_202107
https://www.nxtbook.com/nxtbooks/aas/st_202106
https://www.nxtbook.com/nxtbooks/aas/st_202105
https://www.nxtbook.com/nxtbooks/aas/st_202104
https://www.nxtbook.com/nxtbooks/aas/st_202103
https://www.nxtbook.com/nxtbooks/aas/st_202102
https://www.nxtbook.com/nxtbooks/aas/st_202101
https://www.nxtbook.com/nxtbooks/aas/skywatch_2021
https://www.nxtbook.com/nxtbooks/aas/st_202012
https://www.nxtbook.com/nxtbooks/aas/st_202011
https://www.nxtbook.com/nxtbooks/aas/st_202010
https://www.nxtbook.com/nxtbooks/aas/st_202009
https://www.nxtbook.com/nxtbooks/aas/st_202008
https://www.nxtbook.com/nxtbooks/aas/st_202007
https://www.nxtbook.com/nxtbooks/aas/st_202006
https://www.nxtbook.com/nxtbooks/aas/st_202005
https://www.nxtbook.com/nxtbooks/aas/st_202004
https://www.nxtbook.com/nxtbooks/aas/st_202003
https://www.nxtbook.com/nxtbooks/aas/st_202002
https://www.nxtbook.com/nxtbooks/aas/st_202001
https://www.nxtbook.com/nxtbooks/aas/st_201912
https://www.nxtbook.com/nxtbooks/aas/st_201911
https://www.nxtbook.com/nxtbooks/aas/st_201910
https://www.nxtbook.com/nxtbooks/aas/st_201909
https://www.nxtbook.com/nxtbooks/aas/st_201908
https://www.nxtbook.com/nxtbooks/aas/st_201907
https://www.nxtbook.com/nxtbooks/aas/st_201906
https://www.nxtbook.com/nxtbooks/aas/st_201905
https://www.nxtbook.com/nxtbooks/aas/st_201904
https://www.nxtbook.com/nxtbooks/aas/st_201903
https://www.nxtbook.com/nxtbooks/aas/st_201902
https://www.nxtbook.com/nxtbooks/aas/st_201901
https://www.nxtbook.com/nxtbooks/aas/st_201812
https://www.nxtbook.com/nxtbooks/aas/st_201811
https://www.nxtbook.com/nxtbooks/aas/st_201810
https://www.nxtbook.com/nxtbooks/aas/st_201809
https://www.nxtbook.com/nxtbooks/aas/st_201808
https://www.nxtbook.com/nxtbooks/aas/st_201807
https://www.nxtbook.com/nxtbooks/aas/st_201806
https://www.nxtbook.com/nxtbooks/aas/st_201805
https://www.nxtbook.com/nxtbooks/aas/st_201804
https://www.nxtbook.com/nxtbooks/aas/st_201803
https://www.nxtbook.com/nxtbooks/aas/st_201802
https://www.nxtbook.com/nxtbooks/aas/st_201801
https://www.nxtbook.com/nxtbooks/aas/st_201712
https://www.nxtbook.com/nxtbooks/aas/st_201711
https://www.nxtbook.com/nxtbooks/aas/st_201710
https://www.nxtbook.com/nxtbooks/aas/st_201709
https://www.nxtbook.com/nxtbooks/aas/st_201708
https://www.nxtbook.com/nxtbooks/aas/st_201707
https://www.nxtbook.com/nxtbooks/aas/st_201706
https://www.nxtbook.com/nxtbooks/aas/st_201705
https://www.nxtbook.com/nxtbooks/aas/st_201704
https://www.nxtbook.com/nxtbooks/aas/st_201703
https://www.nxtbook.com/nxtbooks/aas/st_201702
https://www.nxtbook.com/nxtbooks/aas/st_201701
https://www.nxtbook.com/nxtbooks/aas/st_201612
https://www.nxtbook.com/nxtbooks/aas/st_201611
https://www.nxtbook.com/nxtbooks/aas/st_201610
https://www.nxtbook.com/nxtbooks/aas/st_201609
https://www.nxtbook.com/nxtbooks/aas/st_201608
https://www.nxtbook.com/nxtbooks/aas/st_201607
https://www.nxtbook.com/nxtbooks/aas/st_201606
https://www.nxtbook.com/nxtbooks/aas/st_201605
https://www.nxtbook.com/nxtbooks/aas/st_201604
https://www.nxtbook.com/nxtbooks/aas/st_201603
https://www.nxtbook.com/nxtbooks/aas/st_201602
https://www.nxtbook.com/nxtbooks/aas/st_201601
https://www.nxtbook.com/nxtbooks/aas/st_201512
https://www.nxtbook.com/nxtbooks/aas/st_201511
https://www.nxtbook.com/nxtbooks/aas/st_201510
https://www.nxtbook.com/nxtbooks/aas/st_201509
https://www.nxtbook.com/nxtbooks/aas/st_201508
https://www.nxtbook.com/nxtbooks/aas/st_201507
https://www.nxtbook.com/nxtbooks/aas/st_201506
https://www.nxtbook.com/nxtbooks/aas/st_201505
https://www.nxtbook.com/nxtbooks/aas/st_201504
https://www.nxtbook.com/nxtbooks/aas/st_201503
https://www.nxtbook.com/nxtbooks/aas/st_201502
https://www.nxtbook.com/nxtbooks/aas/st_201501
https://www.nxtbook.com/nxtbooks/aas/st_201412
https://www.nxtbook.com/nxtbooks/aas/st_201411
https://www.nxtbook.com/nxtbooks/aas/st_201410
https://www.nxtbook.com/nxtbooks/aas/st_201409
https://www.nxtbook.com/nxtbooks/aas/st_201408
https://www.nxtbook.com/nxtbooks/aas/st_201407
https://www.nxtbook.com/nxtbooks/aas/st_201406
https://www.nxtbook.com/nxtbooks/aas/st_mars
https://www.nxtbook.com/nxtbooks/aas/st_201405
https://www.nxtbook.com/nxtbooks/aas/st_201404
https://www.nxtbook.com/nxtbooks/aas/st_201403
https://www.nxtbook.com/nxtbooks/aas/st_201402
https://www.nxtbook.com/nxtbooks/aas/st_201401
https://www.nxtbook.com/nxtbooks/aas/st_201312
https://www.nxtbook.com/nxtbooks/aas/st_201311
https://www.nxtbook.com/nxtbooks/aas/st_201310
https://www.nxtbook.com/nxtbooks/aas/st_201309
https://www.nxtbook.com/nxtbooks/aas/st_201308
https://www.nxtbook.com/nxtbooks/aas/st_201307
https://www.nxtbook.com/nxtbooks/aas/st_201306
https://www.nxtbook.com/nxtbooks/aas/st_201305
https://www.nxtbook.com/nxtbooks/aas/st_201304
https://www.nxtbook.com/nxtbooks/aas/st_201303
https://www.nxtbook.com/nxtbooks/aas/st_201302
https://www.nxtbook.com/nxtbooks/aas/st_201301
https://www.nxtbook.com/nxtbooks/aas/st_201212
https://www.nxtbook.com/nxtbooks/aas/st_201211
https://www.nxtbook.com/nxtbooks/aas/st_201210
https://www.nxtbook.com/nxtbooks/aas/st_201209
https://www.nxtbook.com/nxtbooks/aas/st_201208
https://www.nxtbook.com/nxtbooks/aas/st_201207
https://www.nxtbook.com/nxtbooks/aas/st_201206
https://www.nxtbook.com/nxtbooks/aas/st_201205
https://www.nxtbook.com/nxtbooks/aas/st_201204
https://www.nxtbook.com/nxtbooks/aas/st_201203
https://www.nxtbook.com/nxtbooks/aas/st_201202
https://www.nxtbook.com/nxtbooks/aas/st_201201
https://www.nxtbook.com/nxtbooks/aas/st_201112
https://www.nxtbook.com/nxtbooks/aas/st_201111
https://www.nxtbook.com/nxtbooks/aas/st_201110
https://www.nxtbook.com/nxtbooks/aas/st_201109
https://www.nxtbook.com/nxtbooks/aas/st_201108
https://www.nxtbook.com/nxtbooks/aas/st_201107
https://www.nxtbook.com/nxtbooks/aas/st_201106
https://www.nxtbook.com/nxtbooks/aas/st_201105
https://www.nxtbook.com/nxtbooks/aas/st_201104
https://www.nxtbook.com/nxtbooks/aas/st_201103
https://www.nxtbook.com/nxtbooks/aas/st_201102
https://www.nxtbook.com/nxtbooks/aas/st_201101
https://www.nxtbook.com/nxtbooks/aas/st_201012
https://www.nxtbook.com/nxtbooks/aas/st_201011
https://www.nxtbook.com/nxtbooks/aas/st_201010
https://www.nxtbook.com/nxtbooks/aas/st_201009
https://www.nxtbook.com/nxtbooks/aas/st_201008
https://www.nxtbook.com/nxtbooks/aas/st_201007
https://www.nxtbook.com/nxtbooks/aas/st_201006
https://www.nxtbook.com/nxtbooks/aas/st_201005
https://www.nxtbook.com/nxtbooks/aas/st_201004
https://www.nxtbook.com/nxtbooks/aas/st_201003
https://www.nxtbook.com/nxtbooks/aas/st_201002
https://www.nxtbook.com/nxtbooks/aas/st_201001
https://www.nxtbookmedia.com